diff --git a/account/account.go b/account/account.go
index 4105588f..26f2668f 100644
--- a/account/account.go
+++ b/account/account.go
@@ -38,8 +38,8 @@ func HashSignBytes(chainID string, o Signable) []byte {
 type Account struct {
 	Address     []byte `json:"address"`
 	PubKey      PubKey `json:"pub_key"`
-	Sequence    uint   `json:"sequence"`
-	Balance     uint64 `json:"balance"`
+	Sequence    int    `json:"sequence"`
+	Balance     int64  `json:"balance"`
 	Code        []byte `json:"code"`         // VM code
 	StorageRoot []byte `json:"storage_root"` // VM storage merkle root.
 }
diff --git a/binary/byteslice.go b/binary/byteslice.go
index 87a42785..2e93ab93 100644
--- a/binary/byteslice.go
+++ b/binary/byteslice.go
@@ -10,12 +10,12 @@ const (
 )
 
 func WriteByteSlice(bz []byte, w io.Writer, n *int64, err *error) {
-	WriteUvarint(uint(len(bz)), w, n, err)
+	WriteVarint(len(bz), w, n, err)
 	WriteTo(bz, w, n, err)
 }
 
 func ReadByteSlice(r io.Reader, n *int64, err *error) []byte {
-	length := int(ReadUvarint(r, n, err))
+	length := ReadVarint(r, n, err)
 	if *err != nil {
 		return nil
 	}
@@ -36,7 +36,7 @@ func ReadByteSlice(r io.Reader, n *int64, err *error) []byte {
 //-----------------------------------------------------------------------------
 
 func WriteByteSlices(bzz [][]byte, w io.Writer, n *int64, err *error) {
-	WriteUvarint(uint(len(bzz)), w, n, err)
+	WriteVarint(len(bzz), w, n, err)
 	for _, bz := range bzz {
 		WriteByteSlice(bz, w, n, err)
 		if *err != nil {
@@ -46,7 +46,7 @@ func WriteByteSlices(bzz [][]byte, w io.Writer, n *int64, err *error) {
 }
 
 func ReadByteSlices(r io.Reader, n *int64, err *error) [][]byte {
-	length := int(ReadUvarint(r, n, err))
+	length := ReadVarint(r, n, err)
 	if *err != nil {
 		return nil
 	}
diff --git a/binary/int.go b/binary/int.go
index d35c82bf..3be5f224 100644
--- a/binary/int.go
+++ b/binary/int.go
@@ -219,6 +219,9 @@ func ReadVarint(r io.Reader, n *int64, err *error) int {
 		return 0
 	}
 	if size == 0 {
+		if negate {
+			setFirstErr(err, errors.New("Varint does not allow negative zero"))
+		}
 		return 0
 	}
 	buf := make([]byte, 8)
diff --git a/binary/reflect.go b/binary/reflect.go
index f23acb38..6eac5a46 100644
--- a/binary/reflect.go
+++ b/binary/reflect.go
@@ -432,7 +432,7 @@ func writeReflectBinary(rv reflect.Value, rt reflect.Type, opts Options, w io.Wr
 		} else {
 			// Write length
 			length := rv.Len()
-			WriteUvarint(uint(length), w, n, err)
+			WriteVarint(length, w, n, err)
 			// Write elems
 			for i := 0; i < length; i++ {
 				elemRv := rv.Index(i)
diff --git a/blockchain/pool.go b/blockchain/pool.go
index 5c8b280b..1d82136e 100644
--- a/blockchain/pool.go
+++ b/blockchain/pool.go
@@ -36,8 +36,8 @@ var (
 type BlockPool struct {
 	// block requests
 	requestsMtx   sync.Mutex
-	requests      map[uint]*bpRequest
-	height        uint  // the lowest key in requests.
+	requests      map[int]*bpRequest
+	height        int   // the lowest key in requests.
 	numUnassigned int32 // number of requests not yet assigned to a peer
 	numPending    int32 // number of requests pending assignment or block response
 
@@ -52,11 +52,11 @@ type BlockPool struct {
 	running int32 // atomic
 }
 
-func NewBlockPool(start uint, requestsCh chan<- BlockRequest, timeoutsCh chan<- string) *BlockPool {
+func NewBlockPool(start int, requestsCh chan<- BlockRequest, timeoutsCh chan<- string) *BlockPool {
 	return &BlockPool{
 		peers: make(map[string]*bpPeer),
 
-		requests:      make(map[uint]*bpRequest),
+		requests:      make(map[int]*bpRequest),
 		height:        start,
 		numUnassigned: 0,
 		numPending:    0,
@@ -108,7 +108,7 @@ RUN_LOOP:
 	}
 }
 
-func (pool *BlockPool) GetStatus() (uint, int32) {
+func (pool *BlockPool) GetStatus() (int, int32) {
 	pool.requestsMtx.Lock() // Lock
 	defer pool.requestsMtx.Unlock()
 
@@ -146,7 +146,7 @@ func (pool *BlockPool) PopRequest() {
 
 // Invalidates the block at pool.height.
 // Remove the peer and request from others.
-func (pool *BlockPool) RedoRequest(height uint) {
+func (pool *BlockPool) RedoRequest(height int) {
 	pool.requestsMtx.Lock() // Lock
 	defer pool.requestsMtx.Unlock()
 
@@ -165,7 +165,7 @@ func (pool *BlockPool) RedoRequest(height uint) {
 	go requestRoutine(pool, height)
 }
 
-func (pool *BlockPool) hasBlock(height uint) bool {
+func (pool *BlockPool) hasBlock(height int) bool {
 	pool.requestsMtx.Lock() // Lock
 	defer pool.requestsMtx.Unlock()
 
@@ -173,7 +173,7 @@ func (pool *BlockPool) hasBlock(height uint) bool {
 	return request != nil && request.block != nil
 }
 
-func (pool *BlockPool) setPeerForRequest(height uint, peerId string) {
+func (pool *BlockPool) setPeerForRequest(height int, peerId string) {
 	pool.requestsMtx.Lock() // Lock
 	defer pool.requestsMtx.Unlock()
 
@@ -185,7 +185,7 @@ func (pool *BlockPool) setPeerForRequest(height uint, peerId string) {
 	request.peerId = peerId
 }
 
-func (pool *BlockPool) removePeerForRequest(height uint, peerId string) {
+func (pool *BlockPool) removePeerForRequest(height int, peerId string) {
 	pool.requestsMtx.Lock() // Lock
 	defer pool.requestsMtx.Unlock()
 
@@ -224,7 +224,7 @@ func (pool *BlockPool) getPeer(peerId string) *bpPeer {
 }
 
 // Sets the peer's alleged blockchain height.
-func (pool *BlockPool) SetPeerHeight(peerId string, height uint) {
+func (pool *BlockPool) SetPeerHeight(peerId string, height int) {
 	pool.peersMtx.Lock() // Lock
 	defer pool.peersMtx.Unlock()
 
@@ -250,7 +250,7 @@ func (pool *BlockPool) RemovePeer(peerId string) {
 
 // Pick an available peer with at least the given minHeight.
 // If no peers are available, returns nil.
-func (pool *BlockPool) pickIncrAvailablePeer(minHeight uint) *bpPeer {
+func (pool *BlockPool) pickIncrAvailablePeer(minHeight int) *bpPeer {
 	pool.peersMtx.Lock()
 	defer pool.peersMtx.Unlock()
 
@@ -282,7 +282,7 @@ func (pool *BlockPool) makeNextRequest() {
 	pool.requestsMtx.Lock() // Lock
 	defer pool.requestsMtx.Unlock()
 
-	nextHeight := pool.height + uint(len(pool.requests))
+	nextHeight := pool.height + len(pool.requests)
 	request := &bpRequest{
 		height: nextHeight,
 		peerId: "",
@@ -296,7 +296,7 @@ func (pool *BlockPool) makeNextRequest() {
 	go requestRoutine(pool, nextHeight)
 }
 
-func (pool *BlockPool) sendRequest(height uint, peerId string) {
+func (pool *BlockPool) sendRequest(height int, peerId string) {
 	if atomic.LoadInt32(&pool.running) == 0 {
 		return
 	}
@@ -315,7 +315,7 @@ func (pool *BlockPool) debug() string {
 	defer pool.requestsMtx.Unlock()
 
 	str := ""
-	for h := pool.height; h < pool.height+uint(len(pool.requests)); h++ {
+	for h := pool.height; h < pool.height+len(pool.requests); h++ {
 		if pool.requests[h] == nil {
 			str += Fmt("H(%v):X ", h)
 		} else {
@@ -330,12 +330,12 @@ func (pool *BlockPool) debug() string {
 
 type bpPeer struct {
 	id          string
-	height      uint
+	height      int
 	numRequests int32
 }
 
 type bpRequest struct {
-	height uint
+	height int
 	peerId string
 	block  *types.Block
 }
@@ -344,7 +344,7 @@ type bpRequest struct {
 
 // Responsible for making more requests as necessary
 // Returns only when a block is found (e.g. AddBlock() is called)
-func requestRoutine(pool *BlockPool, height uint) {
+func requestRoutine(pool *BlockPool, height int) {
 	for {
 		var peer *bpPeer = nil
 	PICK_LOOP:
@@ -393,6 +393,6 @@ func requestRoutine(pool *BlockPool, height uint) {
 //-------------------------------------
 
 type BlockRequest struct {
-	Height uint
+	Height int
 	PeerId string
 }
diff --git a/blockchain/pool_test.go b/blockchain/pool_test.go
index c07a11d8..e6ff3be4 100644
--- a/blockchain/pool_test.go
+++ b/blockchain/pool_test.go
@@ -11,14 +11,14 @@ import (
 
 type testPeer struct {
 	id     string
-	height uint
+	height int
 }
 
-func makePeers(numPeers int, minHeight, maxHeight uint) map[string]testPeer {
+func makePeers(numPeers int, minHeight, maxHeight int) map[string]testPeer {
 	peers := make(map[string]testPeer, numPeers)
 	for i := 0; i < numPeers; i++ {
 		peerId := RandStr(12)
-		height := minHeight + uint(rand.Intn(int(maxHeight-minHeight)))
+		height := minHeight + rand.Intn(maxHeight-minHeight)
 		peers[peerId] = testPeer{peerId, height}
 	}
 	return peers
@@ -26,7 +26,7 @@ func makePeers(numPeers int, minHeight, maxHeight uint) map[string]testPeer {
 
 func TestBasic(t *testing.T) {
 	peers := makePeers(10, 0, 1000)
-	start := uint(42)
+	start := 42
 	timeoutsCh := make(chan string, 100)
 	requestsCh := make(chan BlockRequest, 100)
 	pool := NewBlockPool(start, requestsCh, timeoutsCh)
@@ -78,7 +78,7 @@ func TestBasic(t *testing.T) {
 
 func TestTimeout(t *testing.T) {
 	peers := makePeers(10, 0, 1000)
-	start := uint(42)
+	start := 42
 	timeoutsCh := make(chan string, 100)
 	requestsCh := make(chan BlockRequest, 100)
 	pool := NewBlockPool(start, requestsCh, timeoutsCh)
diff --git a/blockchain/reactor.go b/blockchain/reactor.go
index 01d0865d..fa7ff693 100644
--- a/blockchain/reactor.go
+++ b/blockchain/reactor.go
@@ -301,7 +301,7 @@ func DecodeMessage(bz []byte) (msgType byte, msg BlockchainMessage, err error) {
 //-------------------------------------
 
 type bcBlockRequestMessage struct {
-	Height uint
+	Height int
 }
 
 func (m *bcBlockRequestMessage) String() string {
@@ -321,7 +321,7 @@ func (m *bcBlockResponseMessage) String() string {
 //-------------------------------------
 
 type bcStatusRequestMessage struct {
-	Height uint
+	Height int
 }
 
 func (m *bcStatusRequestMessage) String() string {
@@ -331,7 +331,7 @@ func (m *bcStatusRequestMessage) String() string {
 //-------------------------------------
 
 type bcStatusResponseMessage struct {
-	Height uint
+	Height int
 }
 
 func (m *bcStatusResponseMessage) String() string {
diff --git a/blockchain/store.go b/blockchain/store.go
index d0618a23..fa7e696e 100644
--- a/blockchain/store.go
+++ b/blockchain/store.go
@@ -25,7 +25,7 @@ well as the Validation.  In the future this may change, perhaps by moving
 the Validation data outside the Block.
 */
 type BlockStore struct {
-	height uint
+	height int
 	db     dbm.DB
 }
 
@@ -38,7 +38,7 @@ func NewBlockStore(db dbm.DB) *BlockStore {
 }
 
 // Height() returns the last known contiguous block height.
-func (bs *BlockStore) Height() uint {
+func (bs *BlockStore) Height() int {
 	return bs.height
 }
 
@@ -50,7 +50,7 @@ func (bs *BlockStore) GetReader(key []byte) io.Reader {
 	return bytes.NewReader(bytez)
 }
 
-func (bs *BlockStore) LoadBlock(height uint) *types.Block {
+func (bs *BlockStore) LoadBlock(height int) *types.Block {
 	var n int64
 	var err error
 	r := bs.GetReader(calcBlockMetaKey(height))
@@ -62,7 +62,7 @@ func (bs *BlockStore) LoadBlock(height uint) *types.Block {
 		panic(Fmt("Error reading block meta: %v", err))
 	}
 	bytez := []byte{}
-	for i := uint(0); i < meta.PartsHeader.Total; i++ {
+	for i := 0; i < meta.PartsHeader.Total; i++ {
 		part := bs.LoadBlockPart(height, i)
 		bytez = append(bytez, part.Bytes...)
 	}
@@ -73,7 +73,7 @@ func (bs *BlockStore) LoadBlock(height uint) *types.Block {
 	return block
 }
 
-func (bs *BlockStore) LoadBlockPart(height uint, index uint) *types.Part {
+func (bs *BlockStore) LoadBlockPart(height int, index int) *types.Part {
 	var n int64
 	var err error
 	r := bs.GetReader(calcBlockPartKey(height, index))
@@ -87,7 +87,7 @@ func (bs *BlockStore) LoadBlockPart(height uint, index uint) *types.Part {
 	return part
 }
 
-func (bs *BlockStore) LoadBlockMeta(height uint) *types.BlockMeta {
+func (bs *BlockStore) LoadBlockMeta(height int) *types.BlockMeta {
 	var n int64
 	var err error
 	r := bs.GetReader(calcBlockMetaKey(height))
@@ -103,7 +103,7 @@ func (bs *BlockStore) LoadBlockMeta(height uint) *types.BlockMeta {
 
 // The +2/3 and other Precommit-votes for block at `height`.
 // This Validation comes from block.LastValidation for `height+1`.
-func (bs *BlockStore) LoadBlockValidation(height uint) *types.Validation {
+func (bs *BlockStore) LoadBlockValidation(height int) *types.Validation {
 	var n int64
 	var err error
 	r := bs.GetReader(calcBlockValidationKey(height))
@@ -118,7 +118,7 @@ func (bs *BlockStore) LoadBlockValidation(height uint) *types.Validation {
 }
 
 // NOTE: the Precommit-vote heights are for the block at `height`
-func (bs *BlockStore) LoadSeenValidation(height uint) *types.Validation {
+func (bs *BlockStore) LoadSeenValidation(height int) *types.Validation {
 	var n int64
 	var err error
 	r := bs.GetReader(calcSeenValidationKey(height))
@@ -152,7 +152,7 @@ func (bs *BlockStore) SaveBlock(block *types.Block, blockParts *types.PartSet, s
 	bs.db.Set(calcBlockMetaKey(height), metaBytes)
 
 	// Save block parts
-	for i := uint(0); i < blockParts.Total(); i++ {
+	for i := 0; i < blockParts.Total(); i++ {
 		bs.saveBlockPart(height, i, blockParts.GetPart(i))
 	}
 
@@ -171,7 +171,7 @@ func (bs *BlockStore) SaveBlock(block *types.Block, blockParts *types.PartSet, s
 	bs.height = height
 }
 
-func (bs *BlockStore) saveBlockPart(height uint, index uint, part *types.Part) {
+func (bs *BlockStore) saveBlockPart(height int, index int, part *types.Part) {
 	if height != bs.height+1 {
 		panic(Fmt("BlockStore can only save contiguous blocks. Wanted %v, got %v", bs.height+1, height))
 	}
@@ -181,19 +181,19 @@ func (bs *BlockStore) saveBlockPart(height uint, index uint, part *types.Part) {
 
 //-----------------------------------------------------------------------------
 
-func calcBlockMetaKey(height uint) []byte {
+func calcBlockMetaKey(height int) []byte {
 	return []byte(fmt.Sprintf("H:%v", height))
 }
 
-func calcBlockPartKey(height uint, partIndex uint) []byte {
+func calcBlockPartKey(height int, partIndex int) []byte {
 	return []byte(fmt.Sprintf("P:%v:%v", height, partIndex))
 }
 
-func calcBlockValidationKey(height uint) []byte {
+func calcBlockValidationKey(height int) []byte {
 	return []byte(fmt.Sprintf("V:%v", height))
 }
 
-func calcSeenValidationKey(height uint) []byte {
+func calcSeenValidationKey(height int) []byte {
 	return []byte(fmt.Sprintf("SV:%v", height))
 }
 
@@ -202,7 +202,7 @@ func calcSeenValidationKey(height uint) []byte {
 var blockStoreKey = []byte("blockStore")
 
 type BlockStoreStateJSON struct {
-	Height uint
+	Height int
 }
 
 func (bsj BlockStoreStateJSON) Save(db dbm.DB) {
diff --git a/cmd/barak/barak.go b/cmd/barak/barak.go
index de0a9c62..affe1693 100644
--- a/cmd/barak/barak.go
+++ b/cmd/barak/barak.go
@@ -20,7 +20,7 @@ import (
 type BarakOptions struct {
 	Validators    []Validator
 	ListenAddress string
-	StartNonce    uint64
+	StartNonce    int64
 	Registries    []string
 }
 
@@ -74,7 +74,7 @@ func NewBarakFromOptions(opt *BarakOptions) *Barak {
 type Barak struct {
 	mtx        sync.Mutex
 	pid        int
-	nonce      uint64
+	nonce      int64
 	processes  map[string]*pcm.Process
 	validators []Validator
 	listeners  []net.Listener
@@ -82,7 +82,7 @@ type Barak struct {
 	registries []string
 }
 
-func NewBarak(rootDir string, nonce uint64, validators []Validator) *Barak {
+func NewBarak(rootDir string, nonce int64, validators []Validator) *Barak {
 	return &Barak{
 		pid:        os.Getpid(),
 		nonce:      nonce,
@@ -243,7 +243,7 @@ func (brk *Barak) WritePidFile() {
 	}
 }
 
-func (brk *Barak) CheckIncrNonce(newNonce uint64) error {
+func (brk *Barak) CheckIncrNonce(newNonce int64) error {
 	brk.mtx.Lock()
 	defer brk.mtx.Unlock()
 	if brk.nonce+1 != newNonce {
diff --git a/cmd/barak/types/command.go b/cmd/barak/types/command.go
index 92df4691..074502e0 100644
--- a/cmd/barak/types/command.go
+++ b/cmd/barak/types/command.go
@@ -11,7 +11,7 @@ type AuthCommand struct {
 }
 
 type NoncedCommand struct {
-	Nonce uint64
+	Nonce int64
 	Command
 }
 
diff --git a/cmd/barak/types/responses.go b/cmd/barak/types/responses.go
index 85fc77bc..f8b138d8 100644
--- a/cmd/barak/types/responses.go
+++ b/cmd/barak/types/responses.go
@@ -6,7 +6,7 @@ import (
 
 type ResponseStatus struct {
 	Pid        int
-	Nonce      uint64
+	Nonce      int64
 	Validators []Validator
 }
 
diff --git a/cmd/barak/types/validator.go b/cmd/barak/types/validator.go
index 252f3dc5..2db48609 100644
--- a/cmd/barak/types/validator.go
+++ b/cmd/barak/types/validator.go
@@ -5,6 +5,6 @@ import (
 )
 
 type Validator struct {
-	VotingPower uint64
+	VotingPower int64
 	PubKey      acm.PubKey
 }
diff --git a/cmd/barak/validate.go b/cmd/barak/validate.go
index df7b420b..9653f732 100644
--- a/cmd/barak/validate.go
+++ b/cmd/barak/validate.go
@@ -6,8 +6,8 @@ import (
 )
 
 func validate(signBytes []byte, validators []Validator, signatures []acm.Signature) bool {
-	var signedPower uint64
-	var totalPower uint64
+	var signedPower int64
+	var totalPower int64
 	for i, val := range validators {
 		if val.PubKey.VerifyBytes(signBytes, signatures[i]) {
 			signedPower += val.VotingPower
diff --git a/cmd/debora/commands.go b/cmd/debora/commands.go
index 316e48ee..dfca0737 100644
--- a/cmd/debora/commands.go
+++ b/cmd/debora/commands.go
@@ -104,7 +104,7 @@ func DownloadFile(privKey acm.PrivKey, remote string, command btypes.CommandServ
 
 // Utility method to get nonce from the remote.
 // The next command should include the returned nonce+1 as nonce.
-func GetNonce(remote string) (uint64, error) {
+func GetNonce(remote string) (int64, error) {
 	response, err := GetStatus(remote)
 	return response.Nonce, err
 }
@@ -118,7 +118,7 @@ func GetStatus(remote string) (response btypes.ResponseStatus, err error) {
 }
 
 // Each developer runs this
-func SignCommand(privKey acm.PrivKey, nonce uint64, command btypes.Command) ([]byte, acm.Signature) {
+func SignCommand(privKey acm.PrivKey, nonce int64, command btypes.Command) ([]byte, acm.Signature) {
 	noncedCommand := btypes.NoncedCommand{
 		Nonce:   nonce,
 		Command: command,
diff --git a/cmd/tendermint/gen_tx.go b/cmd/tendermint/gen_tx.go
index d499fad8..4a04e272 100644
--- a/cmd/tendermint/gen_tx.go
+++ b/cmd/tendermint/gen_tx.go
@@ -32,13 +32,17 @@ func getByteSliceFromHex(prompt string) []byte {
 	return bytes
 }
 
-func getUint64(prompt string) uint64 {
+func getInt(prompt string) int {
 	input := getString(prompt)
 	i, err := strconv.Atoi(input)
 	if err != nil {
-		Exit(Fmt("Not a valid uint64 amount: %v\nError: %v\n", input, err))
+		Exit(Fmt("Not a valid int64 amount: %v\nError: %v\n", input, err))
 	}
-	return uint64(i)
+	return i
+}
+
+func getInt64(prompt string) int64 {
+	return int64(getInt(prompt))
 }
 
 func gen_tx() {
@@ -68,16 +72,16 @@ func gen_tx() {
 	}
 
 	// Get the amount to send from src account
-	srcSendAmount := getUint64(Fmt("Enter amount to send from %X (total: %v): ", srcAccountAddress, srcAccountBalanceStr))
+	srcSendAmount := getInt64(Fmt("Enter amount to send from %X (total: %v): ", srcAccountAddress, srcAccountBalanceStr))
 
 	// Get the next sequence of src account
-	srcSendSequence := uint(getUint64(Fmt("Enter next sequence for %X (guess: %v): ", srcAccountAddress, srcAccountSequenceStr)))
+	srcSendSequence := getInt(Fmt("Enter next sequence for %X (guess: %v): ", srcAccountAddress, srcAccountSequenceStr))
 
 	// Get dest address
 	dstAddress := getByteSliceFromHex("Enter destination address: ")
 
 	// Get the amount to send to dst account
-	dstSendAmount := getUint64(Fmt("Enter amount to send to %X: ", dstAddress))
+	dstSendAmount := getInt64(Fmt("Enter amount to send to %X: ", dstAddress))
 
 	// Construct SendTx
 	tx := &types.SendTx{
diff --git a/common/bit_array.go b/common/bit_array.go
index 034beb0f..d478d02e 100644
--- a/common/bit_array.go
+++ b/common/bit_array.go
@@ -9,12 +9,12 @@ import (
 
 type BitArray struct {
 	mtx   sync.Mutex
-	Bits  uint     `json:"bits"`  // NOTE: persisted via reflect, must be exported
+	Bits  int      `json:"bits"`  // NOTE: persisted via reflect, must be exported
 	Elems []uint64 `json:"elems"` // NOTE: persisted via reflect, must be exported
 }
 
 // There is no BitArray whose Size is 0.  Use nil instead.
-func NewBitArray(bits uint) *BitArray {
+func NewBitArray(bits int) *BitArray {
 	if bits == 0 {
 		return nil
 	}
@@ -24,7 +24,7 @@ func NewBitArray(bits uint) *BitArray {
 	}
 }
 
-func (bA *BitArray) Size() uint {
+func (bA *BitArray) Size() int {
 	if bA == nil {
 		return 0
 	}
@@ -32,7 +32,7 @@ func (bA *BitArray) Size() uint {
 }
 
 // NOTE: behavior is undefined if i >= bA.Bits
-func (bA *BitArray) GetIndex(i uint) bool {
+func (bA *BitArray) GetIndex(i int) bool {
 	if bA == nil {
 		return false
 	}
@@ -41,15 +41,15 @@ func (bA *BitArray) GetIndex(i uint) bool {
 	return bA.getIndex(i)
 }
 
-func (bA *BitArray) getIndex(i uint) bool {
+func (bA *BitArray) getIndex(i int) bool {
 	if i >= bA.Bits {
 		return false
 	}
-	return bA.Elems[i/64]&(uint64(1)<<(i%64)) > 0
+	return bA.Elems[i/64]&(uint64(1)<<uint(i%64)) > 0
 }
 
 // NOTE: behavior is undefined if i >= bA.Bits
-func (bA *BitArray) SetIndex(i uint, v bool) bool {
+func (bA *BitArray) SetIndex(i int, v bool) bool {
 	if bA == nil {
 		return false
 	}
@@ -58,14 +58,14 @@ func (bA *BitArray) SetIndex(i uint, v bool) bool {
 	return bA.setIndex(i, v)
 }
 
-func (bA *BitArray) setIndex(i uint, v bool) bool {
+func (bA *BitArray) setIndex(i int, v bool) bool {
 	if i >= bA.Bits {
 		return false
 	}
 	if v {
-		bA.Elems[i/64] |= (uint64(1) << (i % 64))
+		bA.Elems[i/64] |= (uint64(1) << uint(i%64))
 	} else {
-		bA.Elems[i/64] &= ^(uint64(1) << (i % 64))
+		bA.Elems[i/64] &= ^(uint64(1) << uint(i%64))
 	}
 	return true
 }
@@ -88,7 +88,7 @@ func (bA *BitArray) copy() *BitArray {
 	}
 }
 
-func (bA *BitArray) copyBits(bits uint) *BitArray {
+func (bA *BitArray) copyBits(bits int) *BitArray {
 	c := make([]uint64, (bits+63)/64)
 	copy(c, bA.Elems)
 	return &BitArray{
@@ -104,7 +104,7 @@ func (bA *BitArray) Or(o *BitArray) *BitArray {
 	}
 	bA.mtx.Lock()
 	defer bA.mtx.Unlock()
-	c := bA.copyBits(MaxUint(bA.Bits, o.Bits))
+	c := bA.copyBits(MaxInt(bA.Bits, o.Bits))
 	for i := 0; i < len(c.Elems); i++ {
 		c.Elems[i] |= o.Elems[i]
 	}
@@ -122,7 +122,7 @@ func (bA *BitArray) And(o *BitArray) *BitArray {
 }
 
 func (bA *BitArray) and(o *BitArray) *BitArray {
-	c := bA.copyBits(MinUint(bA.Bits, o.Bits))
+	c := bA.copyBits(MinInt(bA.Bits, o.Bits))
 	for i := 0; i < len(c.Elems); i++ {
 		c.Elems[i] &= o.Elems[i]
 	}
@@ -153,7 +153,7 @@ func (bA *BitArray) Sub(o *BitArray) *BitArray {
 		for i := 0; i < len(o.Elems)-1; i++ {
 			c.Elems[i] &= ^c.Elems[i]
 		}
-		i := uint(len(o.Elems) - 1)
+		i := len(o.Elems) - 1
 		if i >= 0 {
 			for idx := i * 64; idx < o.Bits; idx++ {
 				c.setIndex(idx, c.getIndex(idx) && !o.GetIndex(idx))
@@ -182,10 +182,10 @@ func (bA *BitArray) IsFull() bool {
 	// Check that the last element has (lastElemBits) 1's
 	lastElemBits := (bA.Bits+63)%64 + 1
 	lastElem := bA.Elems[len(bA.Elems)-1]
-	return (lastElem+1)&((uint64(1)<<lastElemBits)-1) == 0
+	return (lastElem+1)&((uint64(1)<<uint(lastElemBits))-1) == 0
 }
 
-func (bA *BitArray) PickRandom() (uint, bool) {
+func (bA *BitArray) PickRandom() (int, bool) {
 	if bA == nil {
 		return 0, false
 	}
@@ -205,14 +205,14 @@ func (bA *BitArray) PickRandom() (uint, bool) {
 				for j := 0; j < 64; j++ {
 					bitIdx := ((j + randBitStart) % 64)
 					if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
-						return 64*uint(elemIdx) + uint(bitIdx), true
+						return 64*elemIdx + bitIdx, true
 					}
 				}
 				panic("should not happen")
 			}
 		} else {
 			// Special case for last elem, to ignore straggler bits
-			elemBits := int(bA.Bits) % 64
+			elemBits := bA.Bits % 64
 			if elemBits == 0 {
 				elemBits = 64
 			}
@@ -220,7 +220,7 @@ func (bA *BitArray) PickRandom() (uint, bool) {
 			for j := 0; j < elemBits; j++ {
 				bitIdx := ((j + randBitStart) % elemBits)
 				if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
-					return 64*uint(elemIdx) + uint(bitIdx), true
+					return 64*elemIdx + bitIdx, true
 				}
 			}
 		}
@@ -250,7 +250,7 @@ func (bA *BitArray) stringIndented(indent string) string {
 
 	lines := []string{}
 	bits := ""
-	for i := uint(0); i < bA.Bits; i++ {
+	for i := 0; i < bA.Bits; i++ {
 		if bA.getIndex(i) {
 			bits += "X"
 		} else {
diff --git a/common/bit_array_test.go b/common/bit_array_test.go
index a0a1f397..93274aab 100644
--- a/common/bit_array_test.go
+++ b/common/bit_array_test.go
@@ -4,15 +4,15 @@ import (
 	"testing"
 )
 
-func randBitArray(bits uint) (*BitArray, []byte) {
-	src := RandBytes(int((bits + 7) / 8))
+func randBitArray(bits int) (*BitArray, []byte) {
+	src := RandBytes((bits + 7) / 8)
 	bA := NewBitArray(bits)
-	for i := uint(0); i < uint(len(src)); i++ {
-		for j := uint(0); j < 8; j++ {
+	for i := 0; i < len(src); i++ {
+		for j := 0; j < 8; j++ {
 			if i*8+j >= bits {
 				return bA, src
 			}
-			setBit := src[i]&(1<<j) > 0
+			setBit := src[i]&(1<<uint(j)) > 0
 			bA.SetIndex(i*8+j, setBit)
 		}
 	}
@@ -31,7 +31,7 @@ func TestAnd(t *testing.T) {
 	if len(bA3.Elems) != len(bA2.Elems) {
 		t.Error("Expected min elems length")
 	}
-	for i := uint(0); i < bA3.Bits; i++ {
+	for i := 0; i < bA3.Bits; i++ {
 		expected := bA1.GetIndex(i) && bA2.GetIndex(i)
 		if bA3.GetIndex(i) != expected {
 			t.Error("Wrong bit from bA3", i, bA1.GetIndex(i), bA2.GetIndex(i), bA3.GetIndex(i))
@@ -51,7 +51,7 @@ func TestOr(t *testing.T) {
 	if len(bA3.Elems) != len(bA1.Elems) {
 		t.Error("Expected max elems length")
 	}
-	for i := uint(0); i < bA3.Bits; i++ {
+	for i := 0; i < bA3.Bits; i++ {
 		expected := bA1.GetIndex(i) || bA2.GetIndex(i)
 		if bA3.GetIndex(i) != expected {
 			t.Error("Wrong bit from bA3", i, bA1.GetIndex(i), bA2.GetIndex(i), bA3.GetIndex(i))
@@ -71,7 +71,7 @@ func TestSub1(t *testing.T) {
 	if len(bA3.Elems) != len(bA1.Elems) {
 		t.Error("Expected bA1 elems length")
 	}
-	for i := uint(0); i < bA3.Bits; i++ {
+	for i := 0; i < bA3.Bits; i++ {
 		expected := bA1.GetIndex(i)
 		if bA2.GetIndex(i) {
 			expected = false
@@ -94,7 +94,7 @@ func TestSub2(t *testing.T) {
 	if len(bA3.Elems) != len(bA1.Elems) {
 		t.Error("Expected bA1 elems length")
 	}
-	for i := uint(0); i < bA3.Bits; i++ {
+	for i := 0; i < bA3.Bits; i++ {
 		expected := bA1.GetIndex(i)
 		if i < bA2.Bits && bA2.GetIndex(i) {
 			expected = false
@@ -108,12 +108,12 @@ func TestSub2(t *testing.T) {
 func TestPickRandom(t *testing.T) {
 	for idx := 0; idx < 123; idx++ {
 		bA1 := NewBitArray(123)
-		bA1.SetIndex(uint(idx), true)
+		bA1.SetIndex(idx, true)
 		index, ok := bA1.PickRandom()
 		if !ok {
 			t.Fatal("Expected to pick element but got none")
 		}
-		if index != uint(idx) {
+		if index != idx {
 			t.Fatalf("Expected to pick element at %v but got wrong index", idx)
 		}
 	}
diff --git a/common/int.go b/common/int.go
index c6e85dc6..50e86a07 100644
--- a/common/int.go
+++ b/common/int.go
@@ -37,3 +37,19 @@ func PutUint64BE(dest []byte, i uint64) {
 func GetUint64BE(src []byte) uint64 {
 	return binary.BigEndian.Uint64(src)
 }
+
+func PutInt64LE(dest []byte, i int64) {
+	binary.LittleEndian.PutUint64(dest, uint64(i))
+}
+
+func GetInt64LE(src []byte) int64 {
+	return int64(binary.LittleEndian.Uint64(src))
+}
+
+func PutInt64BE(dest []byte, i int64) {
+	binary.BigEndian.PutUint64(dest, uint64(i))
+}
+
+func GetInt64BE(src []byte) int64 {
+	return int64(binary.BigEndian.Uint64(src))
+}
diff --git a/common/random.go b/common/random.go
index 62a50922..e1d6046d 100644
--- a/common/random.go
+++ b/common/random.go
@@ -62,6 +62,18 @@ func RandUint() uint {
 	return uint(rand.Int())
 }
 
+func RandInt16() int16 {
+	return int16(rand.Uint32() & (1<<16 - 1))
+}
+
+func RandInt32() int32 {
+	return int32(rand.Uint32())
+}
+
+func RandInt64() int64 {
+	return int64(rand.Uint32())<<32 + int64(rand.Uint32())
+}
+
 func RandInt() int {
 	return rand.Int()
 }
diff --git a/common/word.go b/common/word.go
index 264a7dcc..893b136e 100644
--- a/common/word.go
+++ b/common/word.go
@@ -28,9 +28,9 @@ func (w Word256) Compare(other Word256) int {
 	return bytes.Compare(w[:], other[:])
 }
 
-func Uint64ToWord256(i uint64) Word256 {
+func Int64ToWord256(i int64) Word256 {
 	buf := [8]byte{}
-	PutUint64BE(buf[:], i)
+	PutInt64BE(buf[:], i)
 	return LeftPadWord256(buf[:])
 }
 
@@ -44,9 +44,9 @@ func LeftPadWord256(bz []byte) (word Word256) {
 	return
 }
 
-func Uint64FromWord256(word Word256) uint64 {
+func Int64FromWord256(word Word256) int64 {
 	buf := word.Postfix(8)
-	return GetUint64BE(buf)
+	return GetInt64BE(buf)
 }
 
 //-------------------------------------
diff --git a/consensus/height_vote_set.go b/consensus/height_vote_set.go
index 1377c67d..0dce526d 100644
--- a/consensus/height_vote_set.go
+++ b/consensus/height_vote_set.go
@@ -27,39 +27,39 @@ we create a new entry in roundVoteSets but also remember the
 peer to prevent abuse.
 */
 type HeightVoteSet struct {
-	height uint
+	height int
 	valSet *sm.ValidatorSet
 
 	mtx               sync.Mutex
-	round             uint                  // max tracked round
-	roundVoteSets     map[uint]RoundVoteSet // keys: [0...round]
-	peerCatchupRounds map[string]uint       // keys: peer.Key; values: round
+	round             int                  // max tracked round
+	roundVoteSets     map[int]RoundVoteSet // keys: [0...round]
+	peerCatchupRounds map[string]int       // keys: peer.Key; values: round
 }
 
-func NewHeightVoteSet(height uint, valSet *sm.ValidatorSet) *HeightVoteSet {
+func NewHeightVoteSet(height int, valSet *sm.ValidatorSet) *HeightVoteSet {
 	hvs := &HeightVoteSet{
 		height:            height,
 		valSet:            valSet,
-		roundVoteSets:     make(map[uint]RoundVoteSet),
-		peerCatchupRounds: make(map[string]uint),
+		roundVoteSets:     make(map[int]RoundVoteSet),
+		peerCatchupRounds: make(map[string]int),
 	}
 	hvs.addRound(0)
 	hvs.round = 0
 	return hvs
 }
 
-func (hvs *HeightVoteSet) Height() uint {
+func (hvs *HeightVoteSet) Height() int {
 	return hvs.height
 }
 
-func (hvs *HeightVoteSet) Round() uint {
+func (hvs *HeightVoteSet) Round() int {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 	return hvs.round
 }
 
 // Create more RoundVoteSets up to round.
-func (hvs *HeightVoteSet) SetRound(round uint) {
+func (hvs *HeightVoteSet) SetRound(round int) {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 	if hvs.round != 0 && (round < hvs.round+1) {
@@ -74,7 +74,7 @@ func (hvs *HeightVoteSet) SetRound(round uint) {
 	hvs.round = round
 }
 
-func (hvs *HeightVoteSet) addRound(round uint) {
+func (hvs *HeightVoteSet) addRound(round int) {
 	if _, ok := hvs.roundVoteSets[round]; ok {
 		panic("addRound() for an existing round")
 	}
@@ -88,7 +88,7 @@ func (hvs *HeightVoteSet) addRound(round uint) {
 
 // Duplicate votes return added=false, err=nil.
 // By convention, peerKey is "" if origin is self.
-func (hvs *HeightVoteSet) AddByAddress(address []byte, vote *types.Vote, peerKey string) (added bool, index uint, err error) {
+func (hvs *HeightVoteSet) AddByAddress(address []byte, vote *types.Vote, peerKey string) (added bool, index int, err error) {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 	voteSet := hvs.getVoteSet(vote.Round, vote.Type)
@@ -108,13 +108,13 @@ func (hvs *HeightVoteSet) AddByAddress(address []byte, vote *types.Vote, peerKey
 	return
 }
 
-func (hvs *HeightVoteSet) Prevotes(round uint) *VoteSet {
+func (hvs *HeightVoteSet) Prevotes(round int) *VoteSet {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 	return hvs.getVoteSet(round, types.VoteTypePrevote)
 }
 
-func (hvs *HeightVoteSet) Precommits(round uint) *VoteSet {
+func (hvs *HeightVoteSet) Precommits(round int) *VoteSet {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
 	return hvs.getVoteSet(round, types.VoteTypePrecommit)
@@ -125,15 +125,15 @@ func (hvs *HeightVoteSet) Precommits(round uint) *VoteSet {
 func (hvs *HeightVoteSet) POLRound() int {
 	hvs.mtx.Lock()
 	defer hvs.mtx.Unlock()
-	for r := int(hvs.round); r >= 0; r-- {
-		if hvs.getVoteSet(uint(r), types.VoteTypePrevote).HasTwoThirdsMajority() {
-			return int(r)
+	for r := hvs.round; r >= 0; r-- {
+		if hvs.getVoteSet(r, types.VoteTypePrevote).HasTwoThirdsMajority() {
+			return r
 		}
 	}
 	return -1
 }
 
-func (hvs *HeightVoteSet) getVoteSet(round uint, type_ byte) *VoteSet {
+func (hvs *HeightVoteSet) getVoteSet(round int, type_ byte) *VoteSet {
 	rvs, ok := hvs.roundVoteSets[round]
 	if !ok {
 		return nil
@@ -155,7 +155,7 @@ func (hvs *HeightVoteSet) String() string {
 func (hvs *HeightVoteSet) StringIndented(indent string) string {
 	vsStrings := make([]string, 0, (len(hvs.roundVoteSets)+1)*2)
 	// rounds 0 ~ hvs.round inclusive
-	for round := uint(0); round <= hvs.round; round++ {
+	for round := 0; round <= hvs.round; round++ {
 		voteSetString := hvs.roundVoteSets[round].Prevotes.StringShort()
 		vsStrings = append(vsStrings, voteSetString)
 		voteSetString = hvs.roundVoteSets[round].Precommits.StringShort()
diff --git a/consensus/reactor.go b/consensus/reactor.go
index 22c4182c..56a873d3 100644
--- a/consensus/reactor.go
+++ b/consensus/reactor.go
@@ -227,7 +227,7 @@ func (conR *ConsensusReactor) Receive(chId byte, peer *p2p.Peer, msgBytes []byte
 }
 
 // Broadcasts HasVoteMessage to peers that care.
-func (conR *ConsensusReactor) broadcastHasVoteMessage(vote *types.Vote, index uint) {
+func (conR *ConsensusReactor) broadcastHasVoteMessage(vote *types.Vote, index int) {
 	msg := &HasVoteMessage{
 		Height: vote.Height,
 		Round:  vote.Round,
@@ -278,7 +278,7 @@ func makeRoundStepMessages(rs *RoundState) (nrsMsg *NewRoundStepMessage, csMsg *
 		Height: rs.Height,
 		Round:  rs.Round,
 		Step:   rs.Step,
-		SecondsSinceStartTime: uint(time.Now().Sub(rs.StartTime).Seconds()),
+		SecondsSinceStartTime: int(time.Now().Sub(rs.StartTime).Seconds()),
 		LastCommitRound:       rs.LastCommit.Round(),
 	}
 	if rs.Step == RoundStepCommit {
@@ -415,8 +415,8 @@ OUTER_LOOP:
 			if 0 <= rs.Proposal.POLRound {
 				msg := &ProposalPOLMessage{
 					Height:           rs.Height,
-					ProposalPOLRound: uint(rs.Proposal.POLRound),
-					ProposalPOL:      rs.Votes.Prevotes(uint(rs.Proposal.POLRound)).BitArray(),
+					ProposalPOLRound: rs.Proposal.POLRound,
+					ProposalPOL:      rs.Votes.Prevotes(rs.Proposal.POLRound).BitArray(),
 				}
 				peer.Send(DataChannel, msg)
 			}
@@ -482,7 +482,7 @@ OUTER_LOOP:
 			if validation == nil {
 				return false
 			} else if *prsVoteSet == nil {
-				ps.EnsureVoteBitArrays(validation.Height(), uint(len(validation.Precommits)), prs)
+				ps.EnsureVoteBitArrays(validation.Height(), len(validation.Precommits), prs)
 				// We could return true here (useful work was done)
 				// or, we can continue since prsVoteSet is no longer nil.
 				if *prsVoteSet == nil {
@@ -522,7 +522,7 @@ OUTER_LOOP:
 			}
 			// If there are POLPrevotes to send...
 			if 0 <= prs.ProposalPOLRound {
-				if polPrevotes := rs.Votes.Prevotes(uint(prs.ProposalPOLRound)); polPrevotes != nil {
+				if polPrevotes := rs.Votes.Prevotes(prs.ProposalPOLRound); polPrevotes != nil {
 					if trySendVote(polPrevotes, &prs.ProposalPOL) {
 						continue OUTER_LOOP
 					}
@@ -580,8 +580,8 @@ OUTER_LOOP:
 
 // Read only when returned by PeerState.GetRoundState().
 type PeerRoundState struct {
-	Height                   uint                // Height peer is at
-	Round                    uint                // Round peer is at
+	Height                   int                 // Height peer is at
+	Round                    int                 // Round peer is at
 	Step                     RoundStepType       // Step peer is at
 	StartTime                time.Time           // Estimated start of round 0 at this height
 	Proposal                 bool                // True if peer has proposal for this round
@@ -591,7 +591,7 @@ type PeerRoundState struct {
 	ProposalPOL              *BitArray           // nil until ProposalPOLMessage received.
 	Prevotes                 *BitArray           // All votes peer has for this round
 	Precommits               *BitArray           // All precommits peer has for this round
-	LastCommitRound          uint                // Round of commit for last height.
+	LastCommitRound          int                 // Round of commit for last height.
 	LastCommit               *BitArray           // All commit precommits of commit for last height.
 	CatchupCommitRound       int                 // Round that we believe commit round is.
 	CatchupCommit            *BitArray           // All commit precommits peer has for this height
@@ -638,12 +638,12 @@ func (ps *PeerState) SetHasProposal(proposal *Proposal) {
 
 	ps.Proposal = true
 	ps.ProposalBlockPartsHeader = proposal.BlockPartsHeader
-	ps.ProposalBlockParts = NewBitArray(uint(proposal.BlockPartsHeader.Total))
+	ps.ProposalBlockParts = NewBitArray(proposal.BlockPartsHeader.Total)
 	ps.ProposalPOLRound = proposal.POLRound
 	ps.ProposalPOL = nil // Nil until ProposalPOLMessage received.
 }
 
-func (ps *PeerState) SetHasProposalBlockPart(height uint, round uint, index uint) {
+func (ps *PeerState) SetHasProposalBlockPart(height int, round int, index int) {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 
@@ -651,13 +651,13 @@ func (ps *PeerState) SetHasProposalBlockPart(height uint, round uint, index uint
 		return
 	}
 
-	ps.ProposalBlockParts.SetIndex(uint(index), true)
+	ps.ProposalBlockParts.SetIndex(index, true)
 }
 
 // prs: If given, will also update this PeerRoundState copy.
 // NOTE: It's important to make sure that numValidators actually matches
 // what the node sees as the number of validators for height.
-func (ps *PeerState) EnsureVoteBitArrays(height uint, numValidators uint, prs *PeerRoundState) {
+func (ps *PeerState) EnsureVoteBitArrays(height int, numValidators int, prs *PeerRoundState) {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 
@@ -690,14 +690,14 @@ func (ps *PeerState) EnsureVoteBitArrays(height uint, numValidators uint, prs *P
 	}
 }
 
-func (ps *PeerState) SetHasVote(vote *types.Vote, index uint) {
+func (ps *PeerState) SetHasVote(vote *types.Vote, index int) {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 
 	ps.setHasVote(vote.Height, vote.Round, vote.Type, index)
 }
 
-func (ps *PeerState) setHasVote(height uint, round uint, type_ byte, index uint) {
+func (ps *PeerState) setHasVote(height int, round int, type_ byte, index int) {
 	if ps.Height == height+1 && ps.LastCommitRound == round && type_ == types.VoteTypePrecommit {
 		// Special case for LastCommit.
 		ps.LastCommit.SetIndex(index, true)
@@ -711,13 +711,13 @@ func (ps *PeerState) setHasVote(height uint, round uint, type_ byte, index uint)
 	// By here, ps.Height is height.
 	switch type_ {
 	case types.VoteTypePrevote:
-		if ps.ProposalPOLRound == int(round) {
+		if ps.ProposalPOLRound == round {
 			ps.ProposalPOL.SetIndex(index, true)
 		}
 		ps.Prevotes.SetIndex(index, true)
 		log.Debug("SetHasVote", "peer", ps.Key, "prevotes", ps.Prevotes, "index", index)
 	case types.VoteTypePrecommit:
-		if ps.CatchupCommitRound == int(round) {
+		if ps.CatchupCommitRound == round {
 			ps.CatchupCommit.SetIndex(index, true)
 		}
 		ps.Precommits.SetIndex(index, true)
@@ -728,20 +728,20 @@ func (ps *PeerState) setHasVote(height uint, round uint, type_ byte, index uint)
 }
 
 // NOTE: 'round' is what we know to be the commit round for height.
-func (ps *PeerState) EnsureCatchupCommitRound(height, round uint) {
+func (ps *PeerState) EnsureCatchupCommitRound(height, round int) {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 
 	if ps.Height != height {
 		return
 	}
-	if ps.CatchupCommitRound != -1 && ps.CatchupCommitRound != int(round) {
+	if ps.CatchupCommitRound != -1 && ps.CatchupCommitRound != round {
 		panic(Fmt("Conflicting CatchupCommitRound. Height: %v, Orig: %v, New: %v", height, ps.CatchupCommitRound, round))
 	}
-	if ps.CatchupCommitRound == int(round) {
+	if ps.CatchupCommitRound == round {
 		return // Nothing to do!
 	}
-	ps.CatchupCommitRound = int(round)
+	ps.CatchupCommitRound = round
 	ps.CatchupCommit = nil
 }
 
@@ -771,7 +771,7 @@ func (ps *PeerState) ApplyNewRoundStepMessage(msg *NewRoundStepMessage, rs *Roun
 		ps.Prevotes = nil
 		ps.Precommits = nil
 	}
-	if psHeight == msg.Height && psRound != msg.Round && int(msg.Round) == psCatchupCommitRound {
+	if psHeight == msg.Height && psRound != msg.Round && msg.Round == psCatchupCommitRound {
 		// Peer caught up to CatchupCommitRound.
 		// Preserve psCatchupCommit!
 		// NOTE: We prefer to use prs.Precommits if
@@ -823,7 +823,7 @@ func (ps *PeerState) ApplyProposalPOLMessage(msg *ProposalPOLMessage) {
 	if ps.Height != msg.Height {
 		return
 	}
-	if ps.ProposalPOLRound != int(msg.ProposalPOLRound) {
+	if ps.ProposalPOLRound != msg.ProposalPOLRound {
 		return
 	}
 
@@ -871,11 +871,11 @@ func DecodeMessage(bz []byte) (msgType byte, msg ConsensusMessage, err error) {
 
 // For every height/round/step transition
 type NewRoundStepMessage struct {
-	Height                uint
-	Round                 uint
+	Height                int
+	Round                 int
 	Step                  RoundStepType
-	SecondsSinceStartTime uint
-	LastCommitRound       uint
+	SecondsSinceStartTime int
+	LastCommitRound       int
 }
 
 func (m *NewRoundStepMessage) String() string {
@@ -886,7 +886,7 @@ func (m *NewRoundStepMessage) String() string {
 //-------------------------------------
 
 type CommitStepMessage struct {
-	Height           uint
+	Height           int
 	BlockPartsHeader types.PartSetHeader
 	BlockParts       *BitArray
 }
@@ -908,8 +908,8 @@ func (m *ProposalMessage) String() string {
 //-------------------------------------
 
 type ProposalPOLMessage struct {
-	Height           uint
-	ProposalPOLRound uint
+	Height           int
+	ProposalPOLRound int
 	ProposalPOL      *BitArray
 }
 
@@ -920,8 +920,8 @@ func (m *ProposalPOLMessage) String() string {
 //-------------------------------------
 
 type BlockPartMessage struct {
-	Height uint
-	Round  uint
+	Height int
+	Round  int
 	Part   *types.Part
 }
 
@@ -932,7 +932,7 @@ func (m *BlockPartMessage) String() string {
 //-------------------------------------
 
 type VoteMessage struct {
-	ValidatorIndex uint
+	ValidatorIndex int
 	Vote           *types.Vote
 }
 
@@ -943,10 +943,10 @@ func (m *VoteMessage) String() string {
 //-------------------------------------
 
 type HasVoteMessage struct {
-	Height uint
-	Round  uint
+	Height int
+	Round  int
 	Type   byte
-	Index  uint
+	Index  int
 }
 
 func (m *HasVoteMessage) String() string {
diff --git a/consensus/state.go b/consensus/state.go
index 1811c117..b74e9a0d 100644
--- a/consensus/state.go
+++ b/consensus/state.go
@@ -201,8 +201,8 @@ func (rs RoundStepType) String() string {
 
 // Immutable when returned from ConsensusState.GetRoundState()
 type RoundState struct {
-	Height             uint // Height we are working on
-	Round              uint
+	Height             int // Height we are working on
+	Round              int
 	Step               RoundStepType
 	StartTime          time.Time
 	CommitTime         time.Time // Subjective time when +2/3 precommits for Block at Round were found
@@ -210,7 +210,7 @@ type RoundState struct {
 	Proposal           *Proposal
 	ProposalBlock      *types.Block
 	ProposalBlockParts *types.PartSet
-	LockedRound        uint
+	LockedRound        int
 	LockedBlock        *types.Block
 	LockedBlockParts   *types.PartSet
 	Votes              *HeightVoteSet
@@ -299,7 +299,7 @@ func (cs *ConsensusState) reconstructLastCommit(state *sm.State) {
 	lastPrecommits := NewVoteSet(state.LastBlockHeight, 0, types.VoteTypePrecommit, state.LastBondedValidators)
 	seenValidation := cs.blockStore.LoadSeenValidation(state.LastBlockHeight)
 	for idx, precommit := range seenValidation.Precommits {
-		added, _, err := lastPrecommits.AddByIndex(uint(idx), precommit)
+		added, _, err := lastPrecommits.AddByIndex(idx, precommit)
 		if !added || err != nil {
 			panic(Fmt("Failed to reconstruct LastCommit: %v", err))
 		}
@@ -339,7 +339,7 @@ func (cs *ConsensusState) Start() {
 }
 
 // EnterNewRound(height, 0) at cs.StartTime.
-func (cs *ConsensusState) scheduleRound0(height uint) {
+func (cs *ConsensusState) scheduleRound0(height int) {
 	//log.Debug("scheduleRound0", "now", time.Now(), "startTime", cs.StartTime)
 	sleepDuration := cs.StartTime.Sub(time.Now())
 	go func() {
@@ -451,7 +451,7 @@ func (cs *ConsensusState) SetPrivValidator(priv *sm.PrivValidator) {
 // Enter: `timeoutPrecommits` after any +2/3 precommits from (height,round-1)
 // Enter: `startTime = commitTime+timeoutCommit` from NewHeight(height)
 // NOTE: cs.StartTime was already set for height.
-func (cs *ConsensusState) EnterNewRound(height uint, round uint) {
+func (cs *ConsensusState) EnterNewRound(height int, round int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || round < cs.Round || (cs.Round == round && cs.Step != RoundStepNewHeight) {
@@ -483,7 +483,7 @@ func (cs *ConsensusState) EnterNewRound(height uint, round uint) {
 }
 
 // Enter: from NewRound(height,round).
-func (cs *ConsensusState) EnterPropose(height uint, round uint) {
+func (cs *ConsensusState) EnterPropose(height int, round int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPropose <= cs.Step) {
@@ -523,7 +523,7 @@ func (cs *ConsensusState) EnterPropose(height uint, round uint) {
 }
 
 // Decides on the next proposal and sets them onto cs.Proposal*
-func (cs *ConsensusState) decideProposal(height uint, round uint) {
+func (cs *ConsensusState) decideProposal(height int, round int) {
 	var block *types.Block
 	var blockParts *types.PartSet
 
@@ -561,7 +561,7 @@ func (cs *ConsensusState) isProposalComplete() bool {
 	if cs.Proposal.POLRound < 0 {
 		return true
 	} else {
-		return cs.Votes.Prevotes(uint(cs.Proposal.POLRound)).HasTwoThirdsMajority()
+		return cs.Votes.Prevotes(cs.Proposal.POLRound).HasTwoThirdsMajority()
 	}
 }
 
@@ -588,7 +588,7 @@ func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts
 			Height:         cs.Height,
 			Time:           time.Now(),
 			Fees:           0, // TODO fees
-			NumTxs:         uint(len(txs)),
+			NumTxs:         len(txs),
 			LastBlockHash:  cs.state.LastBlockHash,
 			LastBlockParts: cs.state.LastBlockParts,
 			StateHash:      nil, // Will set afterwards.
@@ -615,7 +615,7 @@ func (cs *ConsensusState) createProposalBlock() (block *types.Block, blockParts
 // Enter: any +2/3 prevotes for future round.
 // Prevote for LockedBlock if we're locked, or ProposalBlock if valid.
 // Otherwise vote nil.
-func (cs *ConsensusState) EnterPrevote(height uint, round uint) {
+func (cs *ConsensusState) EnterPrevote(height int, round int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrevote <= cs.Step) {
@@ -636,7 +636,7 @@ func (cs *ConsensusState) EnterPrevote(height uint, round uint) {
 	}*/
 }
 
-func (cs *ConsensusState) doPrevote(height uint, round uint) {
+func (cs *ConsensusState) doPrevote(height int, round int) {
 	// If a block is locked, prevote that.
 	if cs.LockedBlock != nil {
 		log.Debug("EnterPrevote: Block was locked")
@@ -666,7 +666,7 @@ func (cs *ConsensusState) doPrevote(height uint, round uint) {
 }
 
 // Enter: any +2/3 prevotes at next round.
-func (cs *ConsensusState) EnterPrevoteWait(height uint, round uint) {
+func (cs *ConsensusState) EnterPrevoteWait(height int, round int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrevoteWait <= cs.Step) {
@@ -695,7 +695,7 @@ func (cs *ConsensusState) EnterPrevoteWait(height uint, round uint) {
 // Lock & precommit the ProposalBlock if we have enough prevotes for it,
 // else, unlock an existing lock and precommit nil if +2/3 of prevotes were nil,
 // else, precommit locked block or nil otherwise.
-func (cs *ConsensusState) EnterPrecommit(height uint, round uint) {
+func (cs *ConsensusState) EnterPrecommit(height int, round int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrecommit <= cs.Step) {
@@ -768,7 +768,7 @@ func (cs *ConsensusState) EnterPrecommit(height uint, round uint) {
 	// Otherwise, we need to fetch the +2/3 prevoted block.
 	// Unlock and precommit nil.
 	// The +2/3 prevotes for this round is the POL for our unlock.
-	if cs.Votes.POLRound() < int(round) {
+	if cs.Votes.POLRound() < round {
 		panic(Fmt("This POLRound shold be %v but got %", round, cs.Votes.POLRound()))
 	}
 	cs.LockedRound = 0
@@ -783,7 +783,7 @@ func (cs *ConsensusState) EnterPrecommit(height uint, round uint) {
 }
 
 // Enter: any +2/3 precommits for next round.
-func (cs *ConsensusState) EnterPrecommitWait(height uint, round uint) {
+func (cs *ConsensusState) EnterPrecommitWait(height int, round int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || round < cs.Round || (cs.Round == round && RoundStepPrecommitWait <= cs.Step) {
@@ -811,7 +811,7 @@ func (cs *ConsensusState) EnterPrecommitWait(height uint, round uint) {
 }
 
 // Enter: +2/3 precommits for block
-func (cs *ConsensusState) EnterCommit(height uint) {
+func (cs *ConsensusState) EnterCommit(height int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 	if cs.Height != height || RoundStepCommit <= cs.Step {
@@ -865,7 +865,7 @@ func (cs *ConsensusState) EnterCommit(height uint) {
 }
 
 // If we have the block AND +2/3 commits for it, finalize.
-func (cs *ConsensusState) tryFinalizeCommit(height uint) {
+func (cs *ConsensusState) tryFinalizeCommit(height int) {
 	// SANITY CHECK
 	if cs.Height != height {
 		panic(Fmt("tryFinalizeCommit() cs.Height: %v vs height: %v", cs.Height, height))
@@ -883,7 +883,7 @@ func (cs *ConsensusState) tryFinalizeCommit(height uint) {
 }
 
 // Increment height and goto RoundStepNewHeight
-func (cs *ConsensusState) FinalizeCommit(height uint) {
+func (cs *ConsensusState) FinalizeCommit(height int) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 
@@ -950,7 +950,7 @@ func (cs *ConsensusState) SetProposal(proposal *Proposal) error {
 
 	// Verify POLRound, which must be -1 or between 0 and proposal.Round exclusive.
 	if proposal.POLRound != -1 &&
-		(proposal.POLRound < 0 || proposal.Round <= uint(proposal.POLRound)) {
+		(proposal.POLRound < 0 || proposal.Round <= proposal.POLRound) {
 		return ErrInvalidProposalPOLRound
 	}
 
@@ -965,7 +965,7 @@ func (cs *ConsensusState) SetProposal(proposal *Proposal) error {
 }
 
 // NOTE: block is not necessarily valid.
-func (cs *ConsensusState) AddProposalBlockPart(height uint, part *types.Part) (added bool, err error) {
+func (cs *ConsensusState) AddProposalBlockPart(height int, part *types.Part) (added bool, err error) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 
@@ -1001,7 +1001,7 @@ func (cs *ConsensusState) AddProposalBlockPart(height uint, part *types.Part) (a
 	return added, nil
 }
 
-func (cs *ConsensusState) AddVote(address []byte, vote *types.Vote, peerKey string) (added bool, index uint, err error) {
+func (cs *ConsensusState) AddVote(address []byte, vote *types.Vote, peerKey string) (added bool, index int, err error) {
 	cs.mtx.Lock()
 	defer cs.mtx.Unlock()
 
@@ -1010,7 +1010,7 @@ func (cs *ConsensusState) AddVote(address []byte, vote *types.Vote, peerKey stri
 
 //-----------------------------------------------------------------------------
 
-func (cs *ConsensusState) addVote(address []byte, vote *types.Vote, peerKey string) (added bool, index uint, err error) {
+func (cs *ConsensusState) addVote(address []byte, vote *types.Vote, peerKey string) (added bool, index int, err error) {
 	// A precommit for the previous height?
 	if vote.Height+1 == cs.Height && vote.Type == types.VoteTypePrecommit {
 		added, index, err = cs.LastCommit.AddByAddress(address, vote)
@@ -1056,8 +1056,7 @@ func (cs *ConsensusState) addVote(address []byte, vote *types.Vote, peerKey stri
 							cs.EnterPrevoteWait(height, vote.Round)
 						}
 					}()
-				} else if cs.Proposal != nil &&
-					0 <= cs.Proposal.POLRound && uint(cs.Proposal.POLRound) == vote.Round {
+				} else if cs.Proposal != nil && 0 <= cs.Proposal.POLRound && cs.Proposal.POLRound == vote.Round {
 					// If the proposal is now complete, enter prevote of cs.Round.
 					if cs.isProposalComplete() {
 						go cs.EnterPrevote(height, cs.Round)
diff --git a/consensus/test.go b/consensus/test.go
index 397befa0..c105f156 100644
--- a/consensus/test.go
+++ b/consensus/test.go
@@ -18,7 +18,7 @@ func randConsensusState() (*ConsensusState, []*sm.PrivValidator) {
 	return cs, privValidators
 }
 
-func randVoteSet(height uint, round uint, type_ byte, numValidators int, votingPower uint64) (*VoteSet, *sm.ValidatorSet, []*sm.PrivValidator) {
+func randVoteSet(height int, round int, type_ byte, numValidators int, votingPower int64) (*VoteSet, *sm.ValidatorSet, []*sm.PrivValidator) {
 	vals := make([]*sm.Validator, numValidators)
 	privValidators := make([]*sm.PrivValidator, numValidators)
 	for i := 0; i < numValidators; i++ {
diff --git a/consensus/types/proposal.go b/consensus/types/proposal.go
index a3a9f546..1c7d0d70 100644
--- a/consensus/types/proposal.go
+++ b/consensus/types/proposal.go
@@ -17,14 +17,14 @@ var (
 )
 
 type Proposal struct {
-	Height           uint                     `json:"height"`
-	Round            uint                     `json:"round"`
+	Height           int                      `json:"height"`
+	Round            int                      `json:"round"`
 	BlockPartsHeader types.PartSetHeader      `json:"block_parts_header"`
 	POLRound         int                      `json:"pol_round"` // -1 if null.
 	Signature        account.SignatureEd25519 `json:"signature"`
 }
 
-func NewProposal(height uint, round uint, blockPartsHeader types.PartSetHeader, polRound int) *Proposal {
+func NewProposal(height int, round int, blockPartsHeader types.PartSetHeader, polRound int) *Proposal {
 	return &Proposal{
 		Height:           height,
 		Round:            round,
diff --git a/consensus/vote_set.go b/consensus/vote_set.go
index 2227cfe9..c5c0ae0c 100644
--- a/consensus/vote_set.go
+++ b/consensus/vote_set.go
@@ -19,23 +19,23 @@ import (
 // A commit of prior rounds can be added added in lieu of votes/precommits.
 // NOTE: Assumes that the sum total of voting power does not exceed MaxUInt64.
 type VoteSet struct {
-	height uint
-	round  uint
+	height int
+	round  int
 	type_  byte
 
 	mtx           sync.Mutex
 	valSet        *sm.ValidatorSet
-	votes         []*types.Vote     // validator index -> vote
-	votesBitArray *BitArray         // validator index -> has vote?
-	votesByBlock  map[string]uint64 // string(blockHash)+string(blockParts) -> vote sum.
-	totalVotes    uint64
+	votes         []*types.Vote    // validator index -> vote
+	votesBitArray *BitArray        // validator index -> has vote?
+	votesByBlock  map[string]int64 // string(blockHash)+string(blockParts) -> vote sum.
+	totalVotes    int64
 	maj23Hash     []byte
 	maj23Parts    types.PartSetHeader
 	maj23Exists   bool
 }
 
 // Constructs a new VoteSet struct used to accumulate votes for given height/round.
-func NewVoteSet(height uint, round uint, type_ byte, valSet *sm.ValidatorSet) *VoteSet {
+func NewVoteSet(height int, round int, type_ byte, valSet *sm.ValidatorSet) *VoteSet {
 	if height == 0 {
 		panic("Cannot make VoteSet for height == 0, doesn't make sense.")
 	}
@@ -46,12 +46,12 @@ func NewVoteSet(height uint, round uint, type_ byte, valSet *sm.ValidatorSet) *V
 		valSet:        valSet,
 		votes:         make([]*types.Vote, valSet.Size()),
 		votesBitArray: NewBitArray(valSet.Size()),
-		votesByBlock:  make(map[string]uint64),
+		votesByBlock:  make(map[string]int64),
 		totalVotes:    0,
 	}
 }
 
-func (voteSet *VoteSet) Height() uint {
+func (voteSet *VoteSet) Height() int {
 	if voteSet == nil {
 		return 0
 	} else {
@@ -59,7 +59,7 @@ func (voteSet *VoteSet) Height() uint {
 	}
 }
 
-func (voteSet *VoteSet) Round() uint {
+func (voteSet *VoteSet) Round() int {
 	if voteSet == nil {
 		return 0
 	} else {
@@ -67,7 +67,7 @@ func (voteSet *VoteSet) Round() uint {
 	}
 }
 
-func (voteSet *VoteSet) Size() uint {
+func (voteSet *VoteSet) Size() int {
 	if voteSet == nil {
 		return 0
 	} else {
@@ -79,7 +79,7 @@ func (voteSet *VoteSet) Size() uint {
 // Otherwise returns err=ErrVote[UnexpectedStep|InvalidAccount|InvalidSignature|InvalidBlockHash|ConflictingSignature]
 // Duplicate votes return added=false, err=nil.
 // NOTE: vote should not be mutated after adding.
-func (voteSet *VoteSet) AddByIndex(valIndex uint, vote *types.Vote) (added bool, index uint, err error) {
+func (voteSet *VoteSet) AddByIndex(valIndex int, vote *types.Vote) (added bool, index int, err error) {
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 
@@ -90,7 +90,7 @@ func (voteSet *VoteSet) AddByIndex(valIndex uint, vote *types.Vote) (added bool,
 // Otherwise returns err=ErrVote[UnexpectedStep|InvalidAccount|InvalidSignature|InvalidBlockHash|ConflictingSignature]
 // Duplicate votes return added=false, err=nil.
 // NOTE: vote should not be mutated after adding.
-func (voteSet *VoteSet) AddByAddress(address []byte, vote *types.Vote) (added bool, index uint, err error) {
+func (voteSet *VoteSet) AddByAddress(address []byte, vote *types.Vote) (added bool, index int, err error) {
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 
@@ -103,7 +103,7 @@ func (voteSet *VoteSet) AddByAddress(address []byte, vote *types.Vote) (added bo
 	return voteSet.addVote(val, valIndex, vote)
 }
 
-func (voteSet *VoteSet) addByIndex(valIndex uint, vote *types.Vote) (bool, uint, error) {
+func (voteSet *VoteSet) addByIndex(valIndex int, vote *types.Vote) (bool, int, error) {
 	// Ensure that signer is a validator.
 	_, val := voteSet.valSet.GetByIndex(valIndex)
 	if val == nil {
@@ -113,7 +113,7 @@ func (voteSet *VoteSet) addByIndex(valIndex uint, vote *types.Vote) (bool, uint,
 	return voteSet.addVote(val, valIndex, vote)
 }
 
-func (voteSet *VoteSet) addVote(val *sm.Validator, valIndex uint, vote *types.Vote) (bool, uint, error) {
+func (voteSet *VoteSet) addVote(val *sm.Validator, valIndex int, vote *types.Vote) (bool, int, error) {
 
 	// Make sure the step matches. (or that vote is commit && round < voteSet.round)
 	if (vote.Height != voteSet.height) ||
@@ -168,7 +168,7 @@ func (voteSet *VoteSet) BitArray() *BitArray {
 	return voteSet.votesBitArray.Copy()
 }
 
-func (voteSet *VoteSet) GetByIndex(valIndex uint) *types.Vote {
+func (voteSet *VoteSet) GetByIndex(valIndex int) *types.Vote {
 	voteSet.mtx.Lock()
 	defer voteSet.mtx.Unlock()
 	return voteSet.votes[valIndex]
@@ -264,7 +264,7 @@ func (voteSet *VoteSet) MakeValidation() *types.Validation {
 		panic("Cannot MakeValidation() unless a blockhash has +2/3")
 	}
 	precommits := make([]*types.Vote, voteSet.valSet.Size())
-	voteSet.valSet.Iterate(func(valIndex uint, val *sm.Validator) bool {
+	voteSet.valSet.Iterate(func(valIndex int, val *sm.Validator) bool {
 		vote := voteSet.votes[valIndex]
 		if vote == nil {
 			return false
diff --git a/consensus/vote_set_test.go b/consensus/vote_set_test.go
index 46bafed6..d6daab19 100644
--- a/consensus/vote_set_test.go
+++ b/consensus/vote_set_test.go
@@ -15,14 +15,14 @@ import (
 // NOTE: see consensus/test.go for common test methods.
 
 // Convenience: Return new vote with different height
-func withHeight(vote *types.Vote, height uint) *types.Vote {
+func withHeight(vote *types.Vote, height int) *types.Vote {
 	vote = vote.Copy()
 	vote.Height = height
 	return vote
 }
 
 // Convenience: Return new vote with different round
-func withRound(vote *types.Vote, round uint) *types.Vote {
+func withRound(vote *types.Vote, round int) *types.Vote {
 	vote = vote.Copy()
 	vote.Round = round
 	return vote
@@ -56,7 +56,7 @@ func signAddVote(privVal *sm.PrivValidator, vote *types.Vote, voteSet *VoteSet)
 }
 
 func TestAddVote(t *testing.T) {
-	height, round := uint(1), uint(0)
+	height, round := 1, 0
 	voteSet, _, privValidators := randVoteSet(height, round, types.VoteTypePrevote, 10, 1)
 	val0 := privValidators[0]
 
@@ -89,7 +89,7 @@ func TestAddVote(t *testing.T) {
 }
 
 func Test2_3Majority(t *testing.T) {
-	height, round := uint(1), uint(0)
+	height, round := 1, 0
 	voteSet, _, privValidators := randVoteSet(height, round, types.VoteTypePrevote, 10, 1)
 
 	vote := &types.Vote{Height: height, Round: round, Type: types.VoteTypePrevote, BlockHash: nil}
@@ -123,11 +123,11 @@ func Test2_3Majority(t *testing.T) {
 }
 
 func Test2_3MajorityRedux(t *testing.T) {
-	height, round := uint(1), uint(0)
+	height, round := 1, 0
 	voteSet, _, privValidators := randVoteSet(height, round, types.VoteTypePrevote, 100, 1)
 
 	blockHash := CRandBytes(32)
-	blockPartsTotal := uint(123)
+	blockPartsTotal := 123
 	blockParts := types.PartSetHeader{blockPartsTotal, CRandBytes(32)}
 
 	vote := &types.Vote{Height: height, Round: round, Type: types.VoteTypePrevote, BlockHash: blockHash, BlockParts: blockParts}
@@ -190,7 +190,7 @@ func Test2_3MajorityRedux(t *testing.T) {
 }
 
 func TestBadVotes(t *testing.T) {
-	height, round := uint(1), uint(0)
+	height, round := 1, 0
 	voteSet, _, privValidators := randVoteSet(height, round, types.VoteTypePrevote, 10, 1)
 
 	// val0 votes for nil.
@@ -226,7 +226,7 @@ func TestBadVotes(t *testing.T) {
 }
 
 func TestMakeValidation(t *testing.T) {
-	height, round := uint(1), uint(0)
+	height, round := 1, 0
 	voteSet, _, privValidators := randVoteSet(height, round, types.VoteTypePrecommit, 10, 1)
 	blockHash, blockParts := CRandBytes(32), types.PartSetHeader{123, CRandBytes(32)}
 
diff --git a/crawler/crawl.go b/crawler/crawl.go
index b337d320..973b27ee 100644
--- a/crawler/crawl.go
+++ b/crawler/crawl.go
@@ -33,8 +33,8 @@ type Node struct {
 
 	LastSeen     time.Time
 	ChainID      string
-	BlockHeight  uint
-	BlockHistory map[uint]time.Time // when we saw each block
+	BlockHeight  int
+	BlockHistory map[int]time.Time // when we saw each block
 	NetInfo      *rpctypes.ResponseNetInfo
 
 	Validator bool
diff --git a/merkle/iavl_node.go b/merkle/iavl_node.go
index 086283a5..6786e9d2 100644
--- a/merkle/iavl_node.go
+++ b/merkle/iavl_node.go
@@ -13,8 +13,8 @@ import (
 type IAVLNode struct {
 	key       interface{}
 	value     interface{}
-	height    uint8
-	size      uint
+	height    int8
+	size      int
 	hash      []byte
 	leftHash  []byte
 	leftNode  *IAVLNode
@@ -38,8 +38,8 @@ func ReadIAVLNode(t *IAVLTree, r io.Reader, n *int64, err *error) *IAVLNode {
 	node := &IAVLNode{}
 
 	// node header
-	node.height = binary.ReadUint8(r, n, err)
-	node.size = binary.ReadUvarint(r, n, err)
+	node.height = binary.ReadInt8(r, n, err)
+	node.size = binary.ReadVarint(r, n, err)
 	node.key = decodeByteSlice(t.keyCodec, r, n, err)
 
 	if node.height == 0 {
@@ -88,7 +88,7 @@ func (node *IAVLNode) has(t *IAVLTree, key interface{}) (has bool) {
 	}
 }
 
-func (node *IAVLNode) get(t *IAVLTree, key interface{}) (index uint, value interface{}) {
+func (node *IAVLNode) get(t *IAVLTree, key interface{}) (index int, value interface{}) {
 	if node.height == 0 {
 		if t.keyCodec.Compare(node.key, key) == 0 {
 			return 0, node.value
@@ -107,7 +107,7 @@ func (node *IAVLNode) get(t *IAVLTree, key interface{}) (index uint, value inter
 	}
 }
 
-func (node *IAVLNode) getByIndex(t *IAVLTree, index uint) (key interface{}, value interface{}) {
+func (node *IAVLNode) getByIndex(t *IAVLTree, index int) (key interface{}, value interface{}) {
 	if node.height == 0 {
 		if index == 0 {
 			return node.key, node.value
@@ -127,7 +127,7 @@ func (node *IAVLNode) getByIndex(t *IAVLTree, index uint) (key interface{}, valu
 }
 
 // NOTE: sets hashes recursively
-func (node *IAVLNode) hashWithCount(t *IAVLTree) ([]byte, uint) {
+func (node *IAVLNode) hashWithCount(t *IAVLTree) ([]byte, int) {
 	if node.hash != nil {
 		return node.hash, 0
 	}
@@ -147,10 +147,10 @@ func (node *IAVLNode) hashWithCount(t *IAVLTree) ([]byte, uint) {
 }
 
 // NOTE: sets hashes recursively
-func (node *IAVLNode) writeHashBytes(t *IAVLTree, w io.Writer) (n int64, hashCount uint, err error) {
+func (node *IAVLNode) writeHashBytes(t *IAVLTree, w io.Writer) (n int64, hashCount int, err error) {
 	// height & size
-	binary.WriteUint8(node.height, w, &n, &err)
-	binary.WriteUvarint(node.size, w, &n, &err)
+	binary.WriteInt8(node.height, w, &n, &err)
+	binary.WriteVarint(node.size, w, &n, &err)
 	// key is not written for inner nodes, unlike writePersistBytes
 
 	if node.height == 0 {
@@ -210,8 +210,8 @@ func (node *IAVLNode) save(t *IAVLTree) []byte {
 // NOTE: sets hashes recursively
 func (node *IAVLNode) writePersistBytes(t *IAVLTree, w io.Writer) (n int64, err error) {
 	// node header
-	binary.WriteUint8(node.height, w, &n, &err)
-	binary.WriteUvarint(node.size, w, &n, &err)
+	binary.WriteInt8(node.height, w, &n, &err)
+	binary.WriteVarint(node.size, w, &n, &err)
 	// key (unlike writeHashBytes, key is written for inner nodes)
 	encodeByteSlice(node.key, t.keyCodec, w, &n, &err)
 
@@ -365,7 +365,7 @@ func (node *IAVLNode) rotateLeft(t *IAVLTree) *IAVLNode {
 
 // NOTE: mutates height and size
 func (node *IAVLNode) calcHeightAndSize(t *IAVLTree) {
-	node.height = maxUint8(node.getLeftNode(t).height, node.getRightNode(t).height) + 1
+	node.height = maxInt8(node.getLeftNode(t).height, node.getRightNode(t).height) + 1
 	node.size = node.getLeftNode(t).size + node.getRightNode(t).size
 }
 
diff --git a/merkle/iavl_proof.go b/merkle/iavl_proof.go
index b3e3b2a0..4d1b11ab 100644
--- a/merkle/iavl_proof.go
+++ b/merkle/iavl_proof.go
@@ -35,8 +35,8 @@ func (proof *IAVLProof) Verify(keyBytes, valueBytes, rootHash []byte) bool {
 }
 
 type IAVLProofInnerNode struct {
-	Height uint8
-	Size   uint
+	Height int8
+	Size   int
 	Left   []byte
 	Right  []byte
 }
@@ -45,8 +45,8 @@ func (branch IAVLProofInnerNode) Hash(childHash []byte) []byte {
 	hasher := sha256.New()
 	buf := new(bytes.Buffer)
 	n, err := int64(0), error(nil)
-	binary.WriteUint8(branch.Height, buf, &n, &err)
-	binary.WriteUvarint(branch.Size, buf, &n, &err)
+	binary.WriteInt8(branch.Height, buf, &n, &err)
+	binary.WriteVarint(branch.Size, buf, &n, &err)
 	if branch.Left == nil {
 		binary.WriteByteSlice(childHash, buf, &n, &err)
 		binary.WriteByteSlice(branch.Right, buf, &n, &err)
@@ -71,8 +71,8 @@ func (leaf IAVLProofLeafNode) Hash() []byte {
 	hasher := sha256.New()
 	buf := new(bytes.Buffer)
 	n, err := int64(0), error(nil)
-	binary.WriteUint8(0, buf, &n, &err)
-	binary.WriteUvarint(1, buf, &n, &err)
+	binary.WriteInt8(0, buf, &n, &err)
+	binary.WriteVarint(1, buf, &n, &err)
 	binary.WriteByteSlice(leaf.KeyBytes, buf, &n, &err)
 	binary.WriteByteSlice(leaf.ValueBytes, buf, &n, &err)
 	if err != nil {
diff --git a/merkle/iavl_test.go b/merkle/iavl_test.go
index e92bf4dd..ae374773 100644
--- a/merkle/iavl_test.go
+++ b/merkle/iavl_test.go
@@ -60,7 +60,7 @@ func P(n *IAVLNode) string {
 
 func TestUnit(t *testing.T) {
 
-	expectHash := func(tree *IAVLTree, hashCount uint) {
+	expectHash := func(tree *IAVLTree, hashCount int) {
 		// ensure number of new hash calculations is as expected.
 		hash, count := tree.HashWithCount()
 		if count != hashCount {
@@ -78,7 +78,7 @@ func TestUnit(t *testing.T) {
 		}
 	}
 
-	expectSet := func(tree *IAVLTree, i int, repr string, hashCount uint) {
+	expectSet := func(tree *IAVLTree, i int, repr string, hashCount int) {
 		origNode := tree.root
 		updated := tree.Set(i, "")
 		// ensure node was added & structure is as expected.
@@ -91,7 +91,7 @@ func TestUnit(t *testing.T) {
 		tree.root = origNode
 	}
 
-	expectRemove := func(tree *IAVLTree, i int, repr string, hashCount uint) {
+	expectRemove := func(tree *IAVLTree, i int, repr string, hashCount int) {
 		origNode := tree.root
 		value, removed := tree.Remove(i)
 		// ensure node was added & structure is as expected.
@@ -168,7 +168,7 @@ func TestIntegration(t *testing.T) {
 		if !updated {
 			t.Error("should have been updated")
 		}
-		if tree.Size() != uint(i+1) {
+		if tree.Size() != i+1 {
 			t.Error("size was wrong", tree.Size(), i+1)
 		}
 	}
@@ -203,7 +203,7 @@ func TestIntegration(t *testing.T) {
 				t.Error("wrong value")
 			}
 		}
-		if tree.Size() != uint(len(records)-(i+1)) {
+		if tree.Size() != len(records)-(i+1) {
 			t.Error("size was wrong", tree.Size(), (len(records) - (i + 1)))
 		}
 	}
@@ -318,7 +318,7 @@ func BenchmarkImmutableAvlTree(b *testing.B) {
 	// 23000ns/op, 43000ops/s
 	// for i := 0; i < 10000000; i++ {
 	for i := 0; i < 1000000; i++ {
-		t.Set(RandUint64(), "")
+		t.Set(RandInt64(), "")
 	}
 
 	fmt.Println("ok, starting")
@@ -327,7 +327,7 @@ func BenchmarkImmutableAvlTree(b *testing.B) {
 
 	b.StartTimer()
 	for i := 0; i < b.N; i++ {
-		ri := RandUint64()
+		ri := RandInt64()
 		t.Set(ri, "")
 		t.Remove(ri)
 	}
diff --git a/merkle/iavl_tree.go b/merkle/iavl_tree.go
index 66c2ea91..144ae9b6 100644
--- a/merkle/iavl_tree.go
+++ b/merkle/iavl_tree.go
@@ -68,14 +68,14 @@ func (t *IAVLTree) Copy() Tree {
 	}
 }
 
-func (t *IAVLTree) Size() uint {
+func (t *IAVLTree) Size() int {
 	if t.root == nil {
 		return 0
 	}
 	return t.root.size
 }
 
-func (t *IAVLTree) Height() uint8 {
+func (t *IAVLTree) Height() int8 {
 	if t.root == nil {
 		return 0
 	}
@@ -106,7 +106,7 @@ func (t *IAVLTree) Hash() []byte {
 	return hash
 }
 
-func (t *IAVLTree) HashWithCount() ([]byte, uint) {
+func (t *IAVLTree) HashWithCount() ([]byte, int) {
 	if t.root == nil {
 		return nil, 0
 	}
@@ -130,14 +130,14 @@ func (t *IAVLTree) Load(hash []byte) {
 	}
 }
 
-func (t *IAVLTree) Get(key interface{}) (index uint, value interface{}) {
+func (t *IAVLTree) Get(key interface{}) (index int, value interface{}) {
 	if t.root == nil {
 		return 0, nil
 	}
 	return t.root.get(t, key)
 }
 
-func (t *IAVLTree) GetByIndex(index uint) (key interface{}, value interface{}) {
+func (t *IAVLTree) GetByIndex(index int) (key interface{}, value interface{}) {
 	if t.root == nil {
 		return nil, nil
 	}
diff --git a/merkle/simple_tree.go b/merkle/simple_tree.go
index 73465008..941ddb5c 100644
--- a/merkle/simple_tree.go
+++ b/merkle/simple_tree.go
@@ -90,8 +90,8 @@ func SimpleHashFromHashables(items []Hashable) []byte {
 //--------------------------------------------------------------------------------
 
 type SimpleProof struct {
-	Index       uint     `json:"index"`
-	Total       uint     `json:"total"`
+	Index       int      `json:"index"`
+	Total       int      `json:"total"`
 	LeafHash    []byte   `json:"leaf_hash"`
 	InnerHashes [][]byte `json:"inner_hashes"` // Hashes from leaf's sibling to a root's child.
 	RootHash    []byte   `json:"root_hash"`
@@ -103,8 +103,8 @@ func SimpleProofsFromHashables(items []Hashable) (proofs []*SimpleProof) {
 	proofs = make([]*SimpleProof, len(items))
 	for i, trail := range trails {
 		proofs[i] = &SimpleProof{
-			Index:       uint(i),
-			Total:       uint(len(items)),
+			Index:       i,
+			Total:       len(items),
 			LeafHash:    trail.Hash,
 			InnerHashes: trail.FlattenInnerHashes(),
 			RootHash:    root.Hash,
@@ -154,7 +154,7 @@ func (sp *SimpleProof) StringIndented(indent string) string {
 
 // Use the leafHash and innerHashes to get the root merkle hash.
 // If the length of the innerHashes slice isn't exactly correct, the result is nil.
-func computeHashFromInnerHashes(index uint, total uint, leafHash []byte, innerHashes [][]byte) []byte {
+func computeHashFromInnerHashes(index int, total int, leafHash []byte, innerHashes [][]byte) []byte {
 	// Recursive impl.
 	if index >= total {
 		return nil
diff --git a/merkle/simple_tree_test.go b/merkle/simple_tree_test.go
index eabf8f32..5cbf732e 100644
--- a/merkle/simple_tree_test.go
+++ b/merkle/simple_tree_test.go
@@ -15,10 +15,10 @@ func (tI testItem) Hash() []byte {
 
 func TestSimpleProof(t *testing.T) {
 
-	numItems := uint(100)
+	numItems := 100
 
 	items := make([]Hashable, numItems)
-	for i := uint(0); i < numItems; i++ {
+	for i := 0; i < numItems; i++ {
 		items[i] = testItem(RandBytes(32))
 	}
 
diff --git a/merkle/types.go b/merkle/types.go
index 68a46131..87f716c7 100644
--- a/merkle/types.go
+++ b/merkle/types.go
@@ -1,14 +1,14 @@
 package merkle
 
 type Tree interface {
-	Size() (size uint)
-	Height() (height uint8)
+	Size() (size int)
+	Height() (height int8)
 	Has(key interface{}) (has bool)
-	Get(key interface{}) (index uint, value interface{})
-	GetByIndex(index uint) (key interface{}, value interface{})
+	Get(key interface{}) (index int, value interface{})
+	GetByIndex(index int) (key interface{}, value interface{})
 	Set(key interface{}, value interface{}) (updated bool)
 	Remove(key interface{}) (value interface{}, removed bool)
-	HashWithCount() (hash []byte, count uint)
+	HashWithCount() (hash []byte, count int)
 	Hash() (hash []byte)
 	Save() (hash []byte)
 	Load(hash []byte)
diff --git a/merkle/util.go b/merkle/util.go
index edc3fbf7..89fd2741 100644
--- a/merkle/util.go
+++ b/merkle/util.go
@@ -35,7 +35,7 @@ func printIAVLNode(node *IAVLNode, indent int) {
 
 }
 
-func maxUint8(a, b uint8) uint8 {
+func maxInt8(a, b int8) int8 {
 	if a > b {
 		return a
 	}
diff --git a/p2p/addrbook.go b/p2p/addrbook.go
index e558c83b..99aa5cef 100644
--- a/p2p/addrbook.go
+++ b/p2p/addrbook.go
@@ -715,7 +715,7 @@ func groupKey(na *NetAddress) string {
 type knownAddress struct {
 	Addr        *NetAddress
 	Src         *NetAddress
-	Attempts    uint32
+	Attempts    int32
 	LastAttempt time.Time
 	LastSuccess time.Time
 	BucketType  byte
diff --git a/p2p/connection.go b/p2p/connection.go
index 17912925..856f40f3 100644
--- a/p2p/connection.go
+++ b/p2p/connection.go
@@ -441,9 +441,9 @@ FOR_LOOP:
 
 type ChannelDescriptor struct {
 	Id                 byte
-	Priority           uint
-	SendQueueCapacity  uint
-	RecvBufferCapacity uint
+	Priority           int
+	SendQueueCapacity  int
+	RecvBufferCapacity int
 }
 
 func (chDesc *ChannelDescriptor) FillDefaults() {
@@ -462,10 +462,10 @@ type Channel struct {
 	desc          *ChannelDescriptor
 	id            byte
 	sendQueue     chan []byte
-	sendQueueSize uint32 // atomic.
+	sendQueueSize int32 // atomic.
 	recving       []byte
 	sending       []byte
-	priority      uint
+	priority      int
 	recentlySent  int64 // exponential moving average
 }
 
@@ -494,7 +494,7 @@ func (ch *Channel) sendBytes(bytes []byte) bool {
 		// timeout
 		return false
 	case ch.sendQueue <- bytes:
-		atomic.AddUint32(&ch.sendQueueSize, 1)
+		atomic.AddInt32(&ch.sendQueueSize, 1)
 		return true
 	}
 }
@@ -505,7 +505,7 @@ func (ch *Channel) sendBytes(bytes []byte) bool {
 func (ch *Channel) trySendBytes(bytes []byte) bool {
 	select {
 	case ch.sendQueue <- bytes:
-		atomic.AddUint32(&ch.sendQueueSize, 1)
+		atomic.AddInt32(&ch.sendQueueSize, 1)
 		return true
 	default:
 		return false
@@ -514,7 +514,7 @@ func (ch *Channel) trySendBytes(bytes []byte) bool {
 
 // Goroutine-safe
 func (ch *Channel) loadSendQueueSize() (size int) {
-	return int(atomic.LoadUint32(&ch.sendQueueSize))
+	return int(atomic.LoadInt32(&ch.sendQueueSize))
 }
 
 // Goroutine-safe
@@ -545,7 +545,7 @@ func (ch *Channel) nextMsgPacket() msgPacket {
 	if len(ch.sending) <= maxMsgPacketSize {
 		packet.EOF = byte(0x01)
 		ch.sending = nil
-		atomic.AddUint32(&ch.sendQueueSize, ^uint32(0)) // decrement sendQueueSize
+		atomic.AddInt32(&ch.sendQueueSize, -1) // decrement sendQueueSize
 	} else {
 		packet.EOF = byte(0x00)
 		ch.sending = ch.sending[MinInt(maxMsgPacketSize, len(ch.sending)):]
diff --git a/rpc/core/accounts.go b/rpc/core/accounts.go
index e102e1b7..167f0ca5 100644
--- a/rpc/core/accounts.go
+++ b/rpc/core/accounts.go
@@ -44,7 +44,7 @@ func GetStorage(address, key []byte) (*ctypes.ResponseGetStorage, error) {
 }
 
 func ListAccounts() (*ctypes.ResponseListAccounts, error) {
-	var blockHeight uint
+	var blockHeight int
 	var accounts []*acm.Account
 	state := consensusState.GetState()
 	blockHeight = state.LastBlockHeight
diff --git a/rpc/core/blocks.go b/rpc/core/blocks.go
index 4479e926..3a5bbdfb 100644
--- a/rpc/core/blocks.go
+++ b/rpc/core/blocks.go
@@ -9,14 +9,14 @@ import (
 
 //-----------------------------------------------------------------------------
 
-func BlockchainInfo(minHeight, maxHeight uint) (*ctypes.ResponseBlockchainInfo, error) {
+func BlockchainInfo(minHeight, maxHeight int) (*ctypes.ResponseBlockchainInfo, error) {
 	if maxHeight == 0 {
 		maxHeight = blockStore.Height()
 	} else {
-		maxHeight = MinUint(blockStore.Height(), maxHeight)
+		maxHeight = MinInt(blockStore.Height(), maxHeight)
 	}
 	if minHeight == 0 {
-		minHeight = uint(MaxInt(1, int(maxHeight)-20))
+		minHeight = MaxInt(1, maxHeight-20)
 	}
 	log.Debug("BlockchainInfoHandler", "maxHeight", maxHeight, "minHeight", minHeight)
 
@@ -31,7 +31,7 @@ func BlockchainInfo(minHeight, maxHeight uint) (*ctypes.ResponseBlockchainInfo,
 
 //-----------------------------------------------------------------------------
 
-func GetBlock(height uint) (*ctypes.ResponseGetBlock, error) {
+func GetBlock(height int) (*ctypes.ResponseGetBlock, error) {
 	if height == 0 {
 		return nil, fmt.Errorf("height must be greater than 0")
 	}
diff --git a/rpc/core/consensus.go b/rpc/core/consensus.go
index 059bc64a..b97c6155 100644
--- a/rpc/core/consensus.go
+++ b/rpc/core/consensus.go
@@ -8,17 +8,17 @@ import (
 )
 
 func ListValidators() (*ctypes.ResponseListValidators, error) {
-	var blockHeight uint
+	var blockHeight int
 	var bondedValidators []*sm.Validator
 	var unbondingValidators []*sm.Validator
 
 	state := consensusState.GetState()
 	blockHeight = state.LastBlockHeight
-	state.BondedValidators.Iterate(func(index uint, val *sm.Validator) bool {
+	state.BondedValidators.Iterate(func(index int, val *sm.Validator) bool {
 		bondedValidators = append(bondedValidators, val)
 		return false
 	})
-	state.UnbondingValidators.Iterate(func(index uint, val *sm.Validator) bool {
+	state.UnbondingValidators.Iterate(func(index int, val *sm.Validator) bool {
 		unbondingValidators = append(unbondingValidators, val)
 		return false
 	})
diff --git a/rpc/core/mempool.go b/rpc/core/mempool.go
index c9e83b3d..140cf099 100644
--- a/rpc/core/mempool.go
+++ b/rpc/core/mempool.go
@@ -23,7 +23,7 @@ func BroadcastTx(tx types.Tx) (*ctypes.Receipt, error) {
 	if callTx, ok := tx.(*types.CallTx); ok {
 		if len(callTx.Address) == 0 {
 			createsContract = 1
-			contractAddr = state.NewContractAddress(callTx.Input.Address, uint64(callTx.Input.Sequence))
+			contractAddr = state.NewContractAddress(callTx.Input.Address, callTx.Input.Sequence)
 		}
 	}
 	return &ctypes.Receipt{txHash, createsContract, contractAddr}, nil
diff --git a/rpc/core/names.go b/rpc/core/names.go
index 7f0d872e..01c7cef1 100644
--- a/rpc/core/names.go
+++ b/rpc/core/names.go
@@ -17,7 +17,7 @@ func GetName(name string) (*types.NameRegEntry, error) {
 }
 
 func ListNames() (*ctypes.ResponseListNames, error) {
-	var blockHeight uint
+	var blockHeight int
 	var names []*types.NameRegEntry
 	state := consensusState.GetState()
 	blockHeight = state.LastBlockHeight
diff --git a/rpc/core/txs.go b/rpc/core/txs.go
index be269f47..8a80cd4e 100644
--- a/rpc/core/txs.go
+++ b/rpc/core/txs.go
@@ -15,7 +15,7 @@ func toVMAccount(acc *account.Account) *vm.Account {
 		Address:     LeftPadWord256(acc.Address),
 		Balance:     acc.Balance,
 		Code:        acc.Code, // This is crazy.
-		Nonce:       uint64(acc.Sequence),
+		Nonce:       int64(acc.Sequence),
 		StorageRoot: LeftPadWord256(acc.StorageRoot),
 		Other:       acc.PubKey,
 	}
@@ -36,14 +36,14 @@ func Call(address, data []byte) (*ctypes.ResponseCall, error) {
 	caller := &vm.Account{Address: Zero256}
 	txCache := state.NewTxCache(cache)
 	params := vm.Params{
-		BlockHeight: uint64(st.LastBlockHeight),
+		BlockHeight: int64(st.LastBlockHeight),
 		BlockHash:   LeftPadWord256(st.LastBlockHash),
 		BlockTime:   st.LastBlockTime.Unix(),
 		GasLimit:    10000000,
 	}
 
 	vmach := vm.NewVM(txCache, params, caller.Address, nil)
-	gas := uint64(1000000000)
+	gas := int64(1000000000)
 	ret, err := vmach.Call(caller, callee, callee.Code, data, 0, &gas)
 	if err != nil {
 		return nil, err
@@ -61,14 +61,14 @@ func CallCode(code, data []byte) (*ctypes.ResponseCall, error) {
 	caller := &vm.Account{Address: Zero256}
 	txCache := state.NewTxCache(cache)
 	params := vm.Params{
-		BlockHeight: uint64(st.LastBlockHeight),
+		BlockHeight: int64(st.LastBlockHeight),
 		BlockHash:   LeftPadWord256(st.LastBlockHash),
 		BlockTime:   st.LastBlockTime.Unix(),
 		GasLimit:    10000000,
 	}
 
 	vmach := vm.NewVM(txCache, params, caller.Address, nil)
-	gas := uint64(1000000000)
+	gas := int64(1000000000)
 	ret, err := vmach.Call(caller, callee, code, data, 0, &gas)
 	if err != nil {
 		return nil, err
diff --git a/rpc/core/types/responses.go b/rpc/core/types/responses.go
index 221b9562..02dc267d 100644
--- a/rpc/core/types/responses.go
+++ b/rpc/core/types/responses.go
@@ -13,12 +13,12 @@ type ResponseGetStorage struct {
 
 type ResponseCall struct {
 	Return  []byte `json:"return"`
-	GasUsed uint64 `json:"gas_used"`
+	GasUsed int64  `json:"gas_used"`
 	// TODO ...
 }
 
 type ResponseListAccounts struct {
-	BlockHeight uint               `json:"block_height"`
+	BlockHeight int                `json:"block_height"`
 	Accounts    []*account.Account `json:"accounts"`
 }
 
@@ -33,7 +33,7 @@ type ResponseDumpStorage struct {
 }
 
 type ResponseBlockchainInfo struct {
-	LastHeight uint               `json:"last_height"`
+	LastHeight int                `json:"last_height"`
 	BlockMetas []*types.BlockMeta `json:"block_metas"`
 }
 
@@ -55,7 +55,7 @@ type ResponseStatus struct {
 	GenesisHash       []byte         `json:"genesis_hash"`
 	PubKey            account.PubKey `json:"pub_key"`
 	LatestBlockHash   []byte         `json:"latest_block_hash"`
-	LatestBlockHeight uint           `json:"latest_block_height"`
+	LatestBlockHeight int            `json:"latest_block_height"`
 	LatestBlockTime   int64          `json:"latest_block_time"` // nano
 }
 
@@ -71,7 +71,7 @@ type Peer struct {
 }
 
 type ResponseListValidators struct {
-	BlockHeight         uint            `json:"block_height"`
+	BlockHeight         int             `json:"block_height"`
 	BondedValidators    []*sm.Validator `json:"bonded_validators"`
 	UnbondingValidators []*sm.Validator `json:"unbonding_validators"`
 }
@@ -82,6 +82,6 @@ type ResponseDumpConsensusState struct {
 }
 
 type ResponseListNames struct {
-	BlockHeight uint                  `json:"block_height"`
+	BlockHeight int                   `json:"block_height"`
 	Names       []*types.NameRegEntry `json:"names"`
 }
diff --git a/rpc/server/handlers.go b/rpc/server/handlers.go
index 2180a06b..77ecc5c9 100644
--- a/rpc/server/handlers.go
+++ b/rpc/server/handlers.go
@@ -224,7 +224,7 @@ type WSConnection struct {
 	wsConn      *websocket.Conn
 	writeChan   chan WSResponse
 	quitChan    chan struct{}
-	failedSends uint
+	failedSends int
 	started     uint32
 	stopped     uint32
 
diff --git a/rpc/test/client_ws_test.go b/rpc/test/client_ws_test.go
index a310871b..2ea16c95 100644
--- a/rpc/test/client_ws_test.go
+++ b/rpc/test/client_ws_test.go
@@ -51,7 +51,7 @@ func TestWSBlockchainGrowth(t *testing.T) {
 // send a transaction and validate the events from listening for both sender and receiver
 func TestWSSend(t *testing.T) {
 	toAddr := user[1].Address
-	amt := uint64(100)
+	amt := int64(100)
 
 	con := newWSCon(t)
 	eidInput := types.EventStringAccInput(user[0].Address)
@@ -79,7 +79,7 @@ func TestWSDoubleFire(t *testing.T) {
 		unsubscribe(t, con, eid)
 		con.Close()
 	}()
-	amt := uint64(100)
+	amt := int64(100)
 	toAddr := user[1].Address
 	// broadcast the transaction, wait to hear about it
 	waitForEvent(t, con, eid, true, func() {
@@ -104,7 +104,7 @@ func TestWSCallWait(t *testing.T) {
 		unsubscribe(t, con, eid1)
 		con.Close()
 	}()
-	amt, gasLim, fee := uint64(10000), uint64(1000), uint64(1000)
+	amt, gasLim, fee := int64(10000), int64(1000), int64(1000)
 	code, returnCode, returnVal := simpleContract()
 	var contractAddr []byte
 	// wait for the contract to be created
@@ -115,7 +115,7 @@ func TestWSCallWait(t *testing.T) {
 	}, unmarshalValidateCall(amt, returnCode))
 
 	// susbscribe to the new contract
-	amt = uint64(10001)
+	amt = int64(10001)
 	eid2 := types.EventStringAccOutput(contractAddr)
 	subscribe(t, con, eid2)
 	defer func() {
@@ -134,7 +134,7 @@ func TestWSCallWait(t *testing.T) {
 // and validate return
 func TestWSCallNoWait(t *testing.T) {
 	con := newWSCon(t)
-	amt, gasLim, fee := uint64(10000), uint64(1000), uint64(1000)
+	amt, gasLim, fee := int64(10000), int64(1000), int64(1000)
 	code, _, returnVal := simpleContract()
 
 	tx := makeDefaultCallTx(t, wsTyp, nil, code, amt, gasLim, fee)
@@ -142,7 +142,7 @@ func TestWSCallNoWait(t *testing.T) {
 	contractAddr := receipt.ContractAddr
 
 	// susbscribe to the new contract
-	amt = uint64(10001)
+	amt = int64(10001)
 	eid := types.EventStringAccOutput(contractAddr)
 	subscribe(t, con, eid)
 	defer func() {
@@ -160,7 +160,7 @@ func TestWSCallNoWait(t *testing.T) {
 // create two contracts, one of which calls the other
 func TestWSCallCall(t *testing.T) {
 	con := newWSCon(t)
-	amt, gasLim, fee := uint64(10000), uint64(1000), uint64(1000)
+	amt, gasLim, fee := int64(10000), int64(1000), int64(1000)
 	code, _, returnVal := simpleContract()
 	txid := new([]byte)
 
@@ -175,7 +175,7 @@ func TestWSCallCall(t *testing.T) {
 	contractAddr2 := receipt.ContractAddr
 
 	// susbscribe to the new contracts
-	amt = uint64(10001)
+	amt = int64(10001)
 	eid1 := types.EventStringAccReceive(contractAddr1)
 	subscribe(t, con, eid1)
 	defer func() {
diff --git a/rpc/test/helpers.go b/rpc/test/helpers.go
index e794ef29..87f905f4 100644
--- a/rpc/test/helpers.go
+++ b/rpc/test/helpers.go
@@ -88,7 +88,7 @@ func init() {
 //-------------------------------------------------------------------------------
 // some default transaction functions
 
-func makeDefaultSendTx(t *testing.T, typ string, addr []byte, amt uint64) *types.SendTx {
+func makeDefaultSendTx(t *testing.T, typ string, addr []byte, amt int64) *types.SendTx {
 	nonce := getNonce(t, typ, user[0].Address)
 	tx := types.NewSendTx()
 	tx.AddInputWithNonce(user[0].PubKey, amt, nonce+1)
@@ -96,20 +96,20 @@ func makeDefaultSendTx(t *testing.T, typ string, addr []byte, amt uint64) *types
 	return tx
 }
 
-func makeDefaultSendTxSigned(t *testing.T, typ string, addr []byte, amt uint64) *types.SendTx {
+func makeDefaultSendTxSigned(t *testing.T, typ string, addr []byte, amt int64) *types.SendTx {
 	tx := makeDefaultSendTx(t, typ, addr, amt)
 	tx.SignInput(chainID, 0, user[0])
 	return tx
 }
 
-func makeDefaultCallTx(t *testing.T, typ string, addr, code []byte, amt, gasLim, fee uint64) *types.CallTx {
+func makeDefaultCallTx(t *testing.T, typ string, addr, code []byte, amt, gasLim, fee int64) *types.CallTx {
 	nonce := getNonce(t, typ, user[0].Address)
 	tx := types.NewCallTxWithNonce(user[0].PubKey, addr, code, amt, gasLim, fee, nonce+1)
 	tx.Sign(chainID, user[0])
 	return tx
 }
 
-func makeDefaultNameTx(t *testing.T, typ string, name, value string, amt, fee uint64) *types.NameTx {
+func makeDefaultNameTx(t *testing.T, typ string, name, value string, amt, fee int64) *types.NameTx {
 	nonce := getNonce(t, typ, user[0].Address)
 	tx := types.NewNameTxWithNonce(user[0].PubKey, name, value, amt, fee, nonce+1)
 	tx.Sign(chainID, user[0])
@@ -120,7 +120,7 @@ func makeDefaultNameTx(t *testing.T, typ string, name, value string, amt, fee ui
 // rpc call wrappers (fail on err)
 
 // get an account's nonce
-func getNonce(t *testing.T, typ string, addr []byte) uint {
+func getNonce(t *testing.T, typ string, addr []byte) int {
 	client := clients[typ]
 	ac, err := client.GetAccount(addr)
 	if err != nil {
diff --git a/rpc/test/tests.go b/rpc/test/tests.go
index b98914cb..215eb9b3 100644
--- a/rpc/test/tests.go
+++ b/rpc/test/tests.go
@@ -45,7 +45,7 @@ func testGetAccount(t *testing.T, typ string) {
 }
 
 func testSignedTx(t *testing.T, typ string) {
-	amt := uint64(100)
+	amt := int64(100)
 	toAddr := user[1].Address
 	testOneSignTx(t, typ, toAddr, amt)
 
@@ -56,7 +56,7 @@ func testSignedTx(t *testing.T, typ string) {
 	testOneSignTx(t, typ, toAddr, amt)
 }
 
-func testOneSignTx(t *testing.T, typ string, addr []byte, amt uint64) {
+func testOneSignTx(t *testing.T, typ string, addr []byte, amt int64) {
 	tx := makeDefaultSendTx(t, typ, addr, amt)
 	tx2 := signTx(t, typ, tx, user[0])
 	tx2hash := account.HashSignBytes(chainID, tx2)
@@ -72,7 +72,7 @@ func testOneSignTx(t *testing.T, typ string, addr []byte, amt uint64) {
 }
 
 func testBroadcastTx(t *testing.T, typ string) {
-	amt := uint64(100)
+	amt := int64(100)
 	toAddr := user[1].Address
 	tx := makeDefaultSendTxSigned(t, typ, toAddr, amt)
 	receipt := broadcastTx(t, typ, tx)
@@ -106,7 +106,7 @@ func testGetStorage(t *testing.T, typ string) {
 		con.Close()
 	}()
 
-	amt, gasLim, fee := uint64(1100), uint64(1000), uint64(1000)
+	amt, gasLim, fee := int64(1100), int64(1000), int64(1000)
 	code := []byte{0x60, 0x5, 0x60, 0x1, 0x55}
 	tx := makeDefaultCallTx(t, typ, nil, code, amt, gasLim, fee)
 	receipt := broadcastTx(t, typ, tx)
@@ -161,7 +161,7 @@ func testCall(t *testing.T, typ string) {
 	client := clients[typ]
 
 	// create the contract
-	amt, gasLim, fee := uint64(6969), uint64(1000), uint64(1000)
+	amt, gasLim, fee := int64(6969), int64(1000), int64(1000)
 	code, _, _ := simpleContract()
 	tx := makeDefaultCallTx(t, typ, nil, code, amt, gasLim, fee)
 	receipt := broadcastTx(t, typ, tx)
@@ -203,8 +203,8 @@ func testNameReg(t *testing.T, typ string) {
 	// since entries ought to be unique and these run against different clients, we append the typ
 	name := "ye_old_domain_name_" + typ
 	data := "if not now, when"
-	fee := uint64(1000)
-	numDesiredBlocks := uint64(2)
+	fee := int64(1000)
+	numDesiredBlocks := int64(2)
 	amt := fee + numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
 
 	tx := makeDefaultNameTx(t, typ, name, data, amt, fee)
@@ -221,7 +221,7 @@ func testNameReg(t *testing.T, typ string) {
 	}
 
 	// update the data as the owner, make sure still there
-	numDesiredBlocks = uint64(2)
+	numDesiredBlocks = int64(2)
 	data = "these are amongst the things I wish to bestow upon the youth of generations come: a safe supply of honey, and a better money. For what else shall they need"
 	amt = fee + numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
 	tx = makeDefaultNameTx(t, typ, name, data, amt, fee)
diff --git a/rpc/test/ws_helpers.go b/rpc/test/ws_helpers.go
index 55d074ae..211493d1 100644
--- a/rpc/test/ws_helpers.go
+++ b/rpc/test/ws_helpers.go
@@ -133,7 +133,7 @@ func unmarshalResponseNewBlock(b []byte) (*types.Block, error) {
 }
 
 func unmarshalValidateBlockchain(t *testing.T, con *websocket.Conn, eid string) {
-	var initBlockN uint
+	var initBlockN int
 	for i := 0; i < 2; i++ {
 		waitForEvent(t, con, eid, true, func() {}, func(eid string, b []byte) error {
 			block, err := unmarshalResponseNewBlock(b)
@@ -143,7 +143,7 @@ func unmarshalValidateBlockchain(t *testing.T, con *websocket.Conn, eid string)
 			if i == 0 {
 				initBlockN = block.Header.Height
 			} else {
-				if block.Header.Height != initBlockN+uint(i) {
+				if block.Header.Height != initBlockN+i {
 					return fmt.Errorf("Expected block %d, got block %d", i, block.Header.Height)
 				}
 			}
@@ -153,7 +153,7 @@ func unmarshalValidateBlockchain(t *testing.T, con *websocket.Conn, eid string)
 	}
 }
 
-func unmarshalValidateSend(amt uint64, toAddr []byte) func(string, []byte) error {
+func unmarshalValidateSend(amt int64, toAddr []byte) func(string, []byte) error {
 	return func(eid string, b []byte) error {
 		// unmarshal and assert correctness
 		var response struct {
@@ -186,7 +186,7 @@ func unmarshalValidateSend(amt uint64, toAddr []byte) func(string, []byte) error
 	}
 }
 
-func unmarshalValidateCall(amt uint64, returnCode []byte) func(string, []byte) error {
+func unmarshalValidateCall(amt int64, returnCode []byte) func(string, []byte) error {
 	return func(eid string, b []byte) error {
 		// unmarshall and assert somethings
 		var response struct {
diff --git a/state/execution.go b/state/execution.go
index c68bf4ea..16b051ba 100644
--- a/state/execution.go
+++ b/state/execution.go
@@ -44,7 +44,7 @@ func execBlock(s *State, block *types.Block, blockPartsHeader types.PartSetHeade
 			return errors.New("Block at height 1 (first block) should have no LastValidation precommits")
 		}
 	} else {
-		if uint(len(block.LastValidation.Precommits)) != s.LastBondedValidators.Size() {
+		if len(block.LastValidation.Precommits) != s.LastBondedValidators.Size() {
 			return errors.New(Fmt("Invalid block validation size. Expected %v, got %v",
 				s.LastBondedValidators.Size(), len(block.LastValidation.Precommits)))
 		}
@@ -60,7 +60,7 @@ func execBlock(s *State, block *types.Block, blockPartsHeader types.PartSetHeade
 		if precommit == nil {
 			continue
 		}
-		_, val := s.LastBondedValidators.GetByIndex(uint(i))
+		_, val := s.LastBondedValidators.GetByIndex(i)
 		if val == nil {
 			panic(Fmt("Failed to fetch validator at index %v", i))
 		}
@@ -101,7 +101,7 @@ func execBlock(s *State, block *types.Block, blockPartsHeader types.PartSetHeade
 	// If any unbonding periods are over,
 	// reward account with bonded coins.
 	toRelease := []*Validator{}
-	s.UnbondingValidators.Iterate(func(index uint, val *Validator) bool {
+	s.UnbondingValidators.Iterate(func(index int, val *Validator) bool {
 		if val.UnbondHeight+unbondingPeriodBlocks < block.Height {
 			toRelease = append(toRelease, val)
 		}
@@ -114,8 +114,8 @@ func execBlock(s *State, block *types.Block, blockPartsHeader types.PartSetHeade
 	// If any validators haven't signed in a while,
 	// unbond them, they have timed out.
 	toTimeout := []*Validator{}
-	s.BondedValidators.Iterate(func(index uint, val *Validator) bool {
-		lastActivityHeight := MaxUint(val.BondHeight, val.LastCommitHeight)
+	s.BondedValidators.Iterate(func(index int, val *Validator) bool {
+		lastActivityHeight := MaxInt(val.BondHeight, val.LastCommitHeight)
 		if lastActivityHeight+validatorTimeoutBlocks < block.Height {
 			log.Info("Validator timeout", "validator", val, "height", block.Height)
 			toTimeout = append(toTimeout, val)
@@ -191,7 +191,7 @@ func checkInputPubKey(acc *account.Account, in *types.TxInput) error {
 	return nil
 }
 
-func validateInputs(accounts map[string]*account.Account, signBytes []byte, ins []*types.TxInput) (total uint64, err error) {
+func validateInputs(accounts map[string]*account.Account, signBytes []byte, ins []*types.TxInput) (total int64, err error) {
 	for _, in := range ins {
 		acc := accounts[string(in.Address)]
 		if acc == nil {
@@ -219,8 +219,8 @@ func validateInput(acc *account.Account, signBytes []byte, in *types.TxInput) (e
 	// Check sequences
 	if acc.Sequence+1 != in.Sequence {
 		return types.ErrTxInvalidSequence{
-			Got:      uint64(in.Sequence),
-			Expected: uint64(acc.Sequence + 1),
+			Got:      in.Sequence,
+			Expected: acc.Sequence + 1,
 		}
 	}
 	// Check amount
@@ -230,7 +230,7 @@ func validateInput(acc *account.Account, signBytes []byte, in *types.TxInput) (e
 	return nil
 }
 
-func validateOutputs(outs []*types.TxOutput) (total uint64, err error) {
+func validateOutputs(outs []*types.TxOutput) (total int64, err error) {
 	for _, out := range outs {
 		// Check TxOutput basic
 		if err := out.ValidateBasic(); err != nil {
@@ -271,7 +271,7 @@ func adjustByOutputs(accounts map[string]*account.Account, outs []*types.TxOutpu
 func ExecTx(blockCache *BlockCache, tx_ types.Tx, runCall bool, evc events.Fireable) error {
 
 	// TODO: do something with fees
-	fees := uint64(0)
+	fees := int64(0)
 	_s := blockCache.State() // hack to access validators and block height
 
 	// Exec tx
@@ -362,14 +362,14 @@ func ExecTx(blockCache *BlockCache, tx_ types.Tx, runCall bool, evc events.Firea
 		if runCall {
 
 			var (
-				gas     uint64      = tx.GasLimit
+				gas     int64       = tx.GasLimit
 				err     error       = nil
 				caller  *vm.Account = toVMAccount(inAcc)
 				callee  *vm.Account = nil
 				code    []byte      = nil
 				txCache             = NewTxCache(blockCache)
 				params              = vm.Params{
-					BlockHeight: uint64(_s.LastBlockHeight),
+					BlockHeight: int64(_s.LastBlockHeight),
 					BlockHash:   LeftPadWord256(_s.LastBlockHash),
 					BlockTime:   _s.LastBlockTime.Unix(),
 					GasLimit:    10000000,
@@ -490,8 +490,8 @@ func ExecTx(blockCache *BlockCache, tx_ types.Tx, runCall bool, evc events.Firea
 
 		// let's say cost of a name for one block is len(data) + 32
 		costPerBlock := types.NameCostPerBlock * types.NameCostPerByte * tx.BaseEntryCost()
-		expiresIn := value / uint64(costPerBlock)
-		lastBlockHeight := uint64(_s.LastBlockHeight)
+		expiresIn := int(value / costPerBlock)
+		lastBlockHeight := _s.LastBlockHeight
 
 		log.Debug("New NameTx", "value", value, "costPerBlock", costPerBlock, "expiresIn", expiresIn, "lastBlock", lastBlockHeight)
 
@@ -530,9 +530,9 @@ func ExecTx(blockCache *BlockCache, tx_ types.Tx, runCall bool, evc events.Firea
 				} else {
 					// since the size of the data may have changed
 					// we use the total amount of "credit"
-					oldCredit := (entry.Expires - lastBlockHeight) * types.BaseEntryCost(entry.Name, entry.Data)
+					oldCredit := int64(entry.Expires-lastBlockHeight) * types.BaseEntryCost(entry.Name, entry.Data)
 					credit := oldCredit + value
-					expiresIn = credit / costPerBlock
+					expiresIn = int(credit / costPerBlock)
 					if expiresIn < types.MinNameRegistrationPeriod {
 						return fmt.Errorf("Names must be registered for at least %d blocks", types.MinNameRegistrationPeriod)
 					}
diff --git a/state/genesis.go b/state/genesis.go
index 2024e211..47576d1e 100644
--- a/state/genesis.go
+++ b/state/genesis.go
@@ -14,12 +14,12 @@ import (
 
 type GenesisAccount struct {
 	Address []byte `json:"address"`
-	Amount  uint64 `json:"amount"`
+	Amount  int64  `json:"amount"`
 }
 
 type GenesisValidator struct {
 	PubKey   account.PubKeyEd25519 `json:"pub_key"`
-	Amount   uint64                `json:"amount"`
+	Amount   int64                 `json:"amount"`
 	UnbondTo []GenesisAccount      `json:"unbond_to"`
 }
 
diff --git a/state/priv_validator.go b/state/priv_validator.go
index 41c8b913..d88f17b8 100644
--- a/state/priv_validator.go
+++ b/state/priv_validator.go
@@ -23,7 +23,7 @@ const (
 	stepPrecommit = 3
 )
 
-func voteToStep(vote *types.Vote) uint8 {
+func voteToStep(vote *types.Vote) int8 {
 	switch vote.Type {
 	case types.VoteTypePrevote:
 		return stepPrevote
@@ -38,9 +38,9 @@ type PrivValidator struct {
 	Address    []byte                 `json:"address"`
 	PubKey     account.PubKeyEd25519  `json:"pub_key"`
 	PrivKey    account.PrivKeyEd25519 `json:"priv_key"`
-	LastHeight uint                   `json:"last_height"`
-	LastRound  uint                   `json:"last_round"`
-	LastStep   uint8                  `json:"last_step"`
+	LastHeight int                    `json:"last_height"`
+	LastRound  int                    `json:"last_round"`
+	LastStep   int8                   `json:"last_step"`
 
 	// For persistence.
 	// Overloaded for testing.
@@ -166,8 +166,8 @@ func (privVal *PrivValidator) SignRebondTx(chainID string, rebondTx *types.Rebon
 
 		// Persist height/round/step
 		privVal.LastHeight = rebondTx.Height
-		privVal.LastRound = math.MaxUint64 // We can't do anything else for this rebondTx.Height.
-		privVal.LastStep = math.MaxUint8
+		privVal.LastRound = math.MaxInt64 // We can't do anything else for this rebondTx.Height.
+		privVal.LastStep = math.MaxInt8
 		privVal.save()
 
 		// Sign
diff --git a/state/state.go b/state/state.go
index e7486b27..c8d5d512 100644
--- a/state/state.go
+++ b/state/state.go
@@ -16,10 +16,10 @@ import (
 
 var (
 	stateKey                     = []byte("stateKey")
-	minBondAmount                = uint64(1)           // TODO adjust
-	defaultAccountsCacheCapacity = 1000                // TODO adjust
-	unbondingPeriodBlocks        = uint(60 * 24 * 365) // TODO probably better to make it time based.
-	validatorTimeoutBlocks       = uint(10)            // TODO adjust
+	minBondAmount                = int64(1)           // TODO adjust
+	defaultAccountsCacheCapacity = 1000               // TODO adjust
+	unbondingPeriodBlocks        = int(60 * 24 * 365) // TODO probably better to make it time based.
+	validatorTimeoutBlocks       = int(10)            // TODO adjust
 )
 
 //-----------------------------------------------------------------------------
@@ -28,7 +28,7 @@ var (
 type State struct {
 	DB                   dbm.DB
 	ChainID              string
-	LastBlockHeight      uint
+	LastBlockHeight      int
 	LastBlockHash        []byte
 	LastBlockParts       types.PartSetHeader
 	LastBlockTime        time.Time
@@ -50,7 +50,7 @@ func LoadState(db dbm.DB) *State {
 	} else {
 		r, n, err := bytes.NewReader(buf), new(int64), new(error)
 		s.ChainID = binary.ReadString(r, n, err)
-		s.LastBlockHeight = binary.ReadUvarint(r, n, err)
+		s.LastBlockHeight = binary.ReadVarint(r, n, err)
 		s.LastBlockHash = binary.ReadByteSlice(r, n, err)
 		s.LastBlockParts = binary.ReadBinary(types.PartSetHeader{}, r, n, err).(types.PartSetHeader)
 		s.LastBlockTime = binary.ReadTime(r, n, err)
@@ -80,7 +80,7 @@ func (s *State) Save() {
 	s.nameReg.Save()
 	buf, n, err := new(bytes.Buffer), new(int64), new(error)
 	binary.WriteString(s.ChainID, buf, n, err)
-	binary.WriteUvarint(s.LastBlockHeight, buf, n, err)
+	binary.WriteVarint(s.LastBlockHeight, buf, n, err)
 	binary.WriteByteSlice(s.LastBlockHash, buf, n, err)
 	binary.WriteBinary(s.LastBlockParts, buf, n, err)
 	binary.WriteTime(s.LastBlockTime, buf, n, err)
diff --git a/state/state_test.go b/state/state_test.go
index 6a221977..7078cea0 100644
--- a/state/state_test.go
+++ b/state/state_test.go
@@ -81,7 +81,7 @@ func makeBlock(t *testing.T, state *State, validation *types.Validation, txs []t
 			Height:         state.LastBlockHeight + 1,
 			Time:           state.LastBlockTime.Add(time.Minute),
 			Fees:           0,
-			NumTxs:         uint(len(txs)),
+			NumTxs:         len(txs),
 			LastBlockHash:  state.LastBlockHash,
 			LastBlockParts: state.LastBlockParts,
 			StateHash:      nil,
@@ -179,7 +179,7 @@ func TestTxSequence(t *testing.T) {
 	// Test a variety of sequence numbers for the tx.
 	// The tx should only pass when i == 1.
 	for i := -1; i < 3; i++ {
-		sequence := acc0.Sequence + uint(i)
+		sequence := acc0.Sequence + i
 		tx := types.NewSendTx()
 		tx.AddInputWithNonce(acc0PubKey, 1, sequence)
 		tx.AddOutput(acc1.Address, 1)
@@ -216,15 +216,15 @@ func TestNameTxs(t *testing.T) {
 	state, privAccounts, _ := RandGenesisState(3, true, 1000, 1, true, 1000)
 
 	types.MinNameRegistrationPeriod = 5
-	startingBlock := uint64(state.LastBlockHeight)
+	startingBlock := state.LastBlockHeight
 
 	// try some bad names. these should all fail
 	names := []string{"", "\n", "123#$%", "\x00", string([]byte{20, 40, 60, 80}), "baffledbythespectacleinallofthisyouseeehesaidwithouteyes", "no spaces please"}
 	data := "something about all this just doesn't feel right."
-	fee := uint64(1000)
-	numDesiredBlocks := uint64(5)
+	fee := int64(1000)
+	numDesiredBlocks := 5
 	for _, name := range names {
-		amt := fee + numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
+		amt := fee + int64(numDesiredBlocks)*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
 		tx, _ := types.NewNameTx(state, privAccounts[0].PubKey, name, data, amt, fee)
 		tx.Sign(state.ChainID, privAccounts[0])
 
@@ -237,7 +237,7 @@ func TestNameTxs(t *testing.T) {
 	name := "hold_it_chum"
 	datas := []string{"cold&warm", "!@#$%^&*()", "<<<>>>>", "because why would you ever need a ~ or a & or even a % in a json file? make your case and we'll talk"}
 	for _, data := range datas {
-		amt := fee + numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
+		amt := fee + int64(numDesiredBlocks)*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
 		tx, _ := types.NewNameTx(state, privAccounts[0].PubKey, name, data, amt, fee)
 		tx.Sign(state.ChainID, privAccounts[0])
 
@@ -246,7 +246,7 @@ func TestNameTxs(t *testing.T) {
 		}
 	}
 
-	validateEntry := func(t *testing.T, entry *types.NameRegEntry, name, data string, addr []byte, expires uint64) {
+	validateEntry := func(t *testing.T, entry *types.NameRegEntry, name, data string, addr []byte, expires int) {
 
 		if entry == nil {
 			t.Fatalf("Could not find name %s", name)
@@ -268,7 +268,7 @@ func TestNameTxs(t *testing.T) {
 	// try a good one, check data, owner, expiry
 	name = "looking_good/karaoke_bar"
 	data = "on this side of neptune there are 1234567890 people: first is OMNIVORE. Or is it. Ok this is pretty restrictive. No exclamations :(. Faces tho :')"
-	amt := fee + numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
+	amt := fee + int64(numDesiredBlocks)*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
 	tx, _ := types.NewNameTx(state, privAccounts[0].PubKey, name, data, amt, fee)
 	tx.Sign(state.ChainID, privAccounts[0])
 	if err := execTxWithState(state, tx, true); err != nil {
@@ -304,7 +304,7 @@ func TestNameTxs(t *testing.T) {
 	validateEntry(t, entry, name, data, privAccounts[0].Address, startingBlock+numDesiredBlocks*3)
 
 	// fail to update it as non-owner
-	state.LastBlockHeight = uint(entry.Expires - 1)
+	state.LastBlockHeight = entry.Expires - 1
 	tx, _ = types.NewNameTx(state, privAccounts[1].PubKey, name, data, amt, fee)
 	tx.Sign(state.ChainID, privAccounts[1])
 	if err := execTxWithState(state, tx, true); err == nil {
@@ -312,27 +312,27 @@ func TestNameTxs(t *testing.T) {
 	}
 
 	// once expires, non-owner succeeds
-	state.LastBlockHeight = uint(entry.Expires)
+	state.LastBlockHeight = entry.Expires
 	tx, _ = types.NewNameTx(state, privAccounts[1].PubKey, name, data, amt, fee)
 	tx.Sign(state.ChainID, privAccounts[1])
 	if err := execTxWithState(state, tx, true); err != nil {
 		t.Fatal(err)
 	}
 	entry = state.GetNameRegEntry(name)
-	validateEntry(t, entry, name, data, privAccounts[1].Address, uint64(state.LastBlockHeight)+numDesiredBlocks)
+	validateEntry(t, entry, name, data, privAccounts[1].Address, state.LastBlockHeight+numDesiredBlocks)
 
 	// update it as new owner, with new data (longer), but keep the expiry!
 	data = "In the beginning there was no thing, not even the beginning. It hadn't been here, no there, nor for that matter anywhere, not especially because it had not to even exist, let alone to not. Nothing especially odd about that."
 	oldCredit := amt - fee
 	numDesiredBlocks = 10
-	amt = fee + (numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data) - oldCredit)
+	amt = fee + (int64(numDesiredBlocks)*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data) - oldCredit)
 	tx, _ = types.NewNameTx(state, privAccounts[1].PubKey, name, data, amt, fee)
 	tx.Sign(state.ChainID, privAccounts[1])
 	if err := execTxWithState(state, tx, true); err != nil {
 		t.Fatal(err)
 	}
 	entry = state.GetNameRegEntry(name)
-	validateEntry(t, entry, name, data, privAccounts[1].Address, uint64(state.LastBlockHeight)+numDesiredBlocks)
+	validateEntry(t, entry, name, data, privAccounts[1].Address, state.LastBlockHeight+numDesiredBlocks)
 
 	// test removal
 	amt = fee
@@ -351,15 +351,15 @@ func TestNameTxs(t *testing.T) {
 	// test removal by key1 after expiry
 	name = "looking_good/karaoke_bar"
 	data = "some data"
-	amt = fee + numDesiredBlocks*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
+	amt = fee + int64(numDesiredBlocks)*types.NameCostPerByte*types.NameCostPerBlock*types.BaseEntryCost(name, data)
 	tx, _ = types.NewNameTx(state, privAccounts[0].PubKey, name, data, amt, fee)
 	tx.Sign(state.ChainID, privAccounts[0])
 	if err := execTxWithState(state, tx, true); err != nil {
 		t.Fatal(err)
 	}
 	entry = state.GetNameRegEntry(name)
-	validateEntry(t, entry, name, data, privAccounts[0].Address, uint64(state.LastBlockHeight)+numDesiredBlocks)
-	state.LastBlockHeight = uint(entry.Expires)
+	validateEntry(t, entry, name, data, privAccounts[0].Address, state.LastBlockHeight+numDesiredBlocks)
+	state.LastBlockHeight = entry.Expires
 
 	amt = fee
 	data = ""
@@ -474,7 +474,7 @@ attack the network, they'll generate the longest chain and outpace attackers.
 network itself requires minimal structure.   Messages are broadcast on a best effort
 basis,   and   nodes   can   leave  and   rejoin   the  network   at  will,  accepting   the   longest
 proof-of-work chain as proof of what happened while they were gone `
-		entryAmount := uint64(10000)
+		entryAmount := int64(10000)
 
 		state := state.Copy()
 		tx := &types.NameTx{
diff --git a/state/test.go b/state/test.go
index 8e0f3520..a235e762 100644
--- a/state/test.go
+++ b/state/test.go
@@ -22,27 +22,27 @@ func Tempfile(prefix string) (*os.File, string) {
 	return file, file.Name()
 }
 
-func RandAccount(randBalance bool, minBalance uint64) (*account.Account, *account.PrivAccount) {
+func RandAccount(randBalance bool, minBalance int64) (*account.Account, *account.PrivAccount) {
 	privAccount := account.GenPrivAccount()
 	acc := &account.Account{
 		Address:  privAccount.PubKey.Address(),
 		PubKey:   privAccount.PubKey,
-		Sequence: RandUint(),
+		Sequence: RandInt(),
 		Balance:  minBalance,
 	}
 	if randBalance {
-		acc.Balance += uint64(RandUint32())
+		acc.Balance += int64(RandUint32())
 	}
 	return acc, privAccount
 }
 
-func RandValidator(randBonded bool, minBonded uint64) (*ValidatorInfo, *Validator, *PrivValidator) {
+func RandValidator(randBonded bool, minBonded int64) (*ValidatorInfo, *Validator, *PrivValidator) {
 	privVal := GenPrivValidator()
 	_, tempFilePath := Tempfile("priv_validator_")
 	privVal.SetFile(tempFilePath)
 	bonded := minBonded
 	if randBonded {
-		bonded += uint64(RandUint32())
+		bonded += int64(RandUint32())
 	}
 	valInfo := &ValidatorInfo{
 		Address: privVal.Address,
@@ -66,7 +66,7 @@ func RandValidator(randBonded bool, minBonded uint64) (*ValidatorInfo, *Validato
 	return valInfo, val, privVal
 }
 
-func RandGenesisState(numAccounts int, randBalance bool, minBalance uint64, numValidators int, randBonded bool, minBonded uint64) (*State, []*account.PrivAccount, []*PrivValidator) {
+func RandGenesisState(numAccounts int, randBalance bool, minBalance int64, numValidators int, randBonded bool, minBonded int64) (*State, []*account.PrivAccount, []*PrivValidator) {
 	db := dbm.NewMemDB()
 	accounts := make([]GenesisAccount, numAccounts)
 	privAccounts := make([]*account.PrivAccount, numAccounts)
diff --git a/state/tx_cache.go b/state/tx_cache.go
index 428959bc..718d6178 100644
--- a/state/tx_cache.go
+++ b/state/tx_cache.go
@@ -68,7 +68,7 @@ func (cache *TxCache) CreateAccount(creator *vm.Account) *vm.Account {
 	nonce := creator.Nonce
 	creator.Nonce += 1
 
-	addr := LeftPadWord256(NewContractAddress(creator.Address.Postfix(20), nonce))
+	addr := LeftPadWord256(NewContractAddress(creator.Address.Postfix(20), int(nonce)))
 
 	// Create account from address.
 	account, removed := vmUnpack(cache.accounts[addr])
@@ -144,10 +144,10 @@ func (cache *TxCache) AddLog(log *vm.Log) {
 //-----------------------------------------------------------------------------
 
 // Convenience function to return address of new contract
-func NewContractAddress(caller []byte, nonce uint64) []byte {
+func NewContractAddress(caller []byte, nonce int) []byte {
 	temp := make([]byte, 32+8)
 	copy(temp, caller)
-	PutUint64BE(temp[32:], nonce)
+	PutInt64BE(temp[32:], int64(nonce))
 	return sha3.Sha3(temp)[:20]
 }
 
@@ -157,7 +157,7 @@ func toVMAccount(acc *ac.Account) *vm.Account {
 		Address:     LeftPadWord256(acc.Address),
 		Balance:     acc.Balance,
 		Code:        acc.Code, // This is crazy.
-		Nonce:       uint64(acc.Sequence),
+		Nonce:       int64(acc.Sequence),
 		StorageRoot: LeftPadWord256(acc.StorageRoot),
 		Other:       acc.PubKey,
 	}
@@ -180,7 +180,7 @@ func toStateAccount(acc *vm.Account) *ac.Account {
 		PubKey:      pubKey,
 		Balance:     acc.Balance,
 		Code:        acc.Code,
-		Sequence:    uint(acc.Nonce),
+		Sequence:    int(acc.Nonce),
 		StorageRoot: storageRoot,
 	}
 }
diff --git a/state/validator.go b/state/validator.go
index 28046d18..46483b59 100644
--- a/state/validator.go
+++ b/state/validator.go
@@ -15,11 +15,11 @@ type ValidatorInfo struct {
 	Address         []byte                `json:"address"`
 	PubKey          account.PubKeyEd25519 `json:"pub_key"`
 	UnbondTo        []*types.TxOutput     `json:"unbond_to"`
-	FirstBondHeight uint                  `json:"first_bond_height"`
-	FirstBondAmount uint64                `json:"first_bond_amount"`
-	DestroyedHeight uint                  `json:"destroyed_height"` // If destroyed
-	DestroyedAmount uint64                `json:"destroyed_amount"` // If destroyed
-	ReleasedHeight  uint                  `json:"released_height"`  // If released
+	FirstBondHeight int                   `json:"first_bond_height"`
+	FirstBondAmount int64                 `json:"first_bond_amount"`
+	DestroyedHeight int                   `json:"destroyed_height"` // If destroyed
+	DestroyedAmount int64                 `json:"destroyed_amount"` // If destroyed
+	ReleasedHeight  int                   `json:"released_height"`  // If released
 }
 
 func (valInfo *ValidatorInfo) Copy() *ValidatorInfo {
@@ -48,10 +48,10 @@ var ValidatorInfoCodec = binary.Codec{
 type Validator struct {
 	Address          []byte                `json:"address"`
 	PubKey           account.PubKeyEd25519 `json:"pub_key"`
-	BondHeight       uint                  `json:"bond_height"`
-	UnbondHeight     uint                  `json:"unbond_height"`
-	LastCommitHeight uint                  `json:"last_commit_height"`
-	VotingPower      uint64                `json:"voting_power"`
+	BondHeight       int                   `json:"bond_height"`
+	UnbondHeight     int                   `json:"unbond_height"`
+	LastCommitHeight int                   `json:"last_commit_height"`
+	VotingPower      int64                 `json:"voting_power"`
 	Accum            int64                 `json:"accum"`
 }
 
diff --git a/state/validator_set.go b/state/validator_set.go
index af626daf..fad0413d 100644
--- a/state/validator_set.go
+++ b/state/validator_set.go
@@ -28,7 +28,7 @@ type ValidatorSet struct {
 
 	// cached (unexported)
 	proposer         *Validator
-	totalVotingPower uint64
+	totalVotingPower int64
 }
 
 func NewValidatorSet(vals []*Validator) *ValidatorSet {
@@ -43,7 +43,7 @@ func NewValidatorSet(vals []*Validator) *ValidatorSet {
 }
 
 // TODO: mind the overflow when times and votingPower shares too large.
-func (valSet *ValidatorSet) IncrementAccum(times uint) {
+func (valSet *ValidatorSet) IncrementAccum(times int) {
 	// Add VotingPower * times to each validator and order into heap.
 	validatorsHeap := NewHeap()
 	for _, val := range valSet.Validators {
@@ -52,7 +52,7 @@ func (valSet *ValidatorSet) IncrementAccum(times uint) {
 	}
 
 	// Decrement the validator with most accum, times times.
-	for i := uint(0); i < times; i++ {
+	for i := 0; i < times; i++ {
 		mostest := validatorsHeap.Peek().(*Validator)
 		if i == times-1 {
 			valSet.proposer = mostest
@@ -82,27 +82,27 @@ func (valSet *ValidatorSet) HasAddress(address []byte) bool {
 	return idx != len(valSet.Validators) && bytes.Compare(valSet.Validators[idx].Address, address) == 0
 }
 
-func (valSet *ValidatorSet) GetByAddress(address []byte) (index uint, val *Validator) {
+func (valSet *ValidatorSet) GetByAddress(address []byte) (index int, val *Validator) {
 	idx := sort.Search(len(valSet.Validators), func(i int) bool {
 		return bytes.Compare(address, valSet.Validators[i].Address) <= 0
 	})
 	if idx != len(valSet.Validators) && bytes.Compare(valSet.Validators[idx].Address, address) == 0 {
-		return uint(idx), valSet.Validators[idx].Copy()
+		return idx, valSet.Validators[idx].Copy()
 	} else {
 		return 0, nil
 	}
 }
 
-func (valSet *ValidatorSet) GetByIndex(index uint) (address []byte, val *Validator) {
+func (valSet *ValidatorSet) GetByIndex(index int) (address []byte, val *Validator) {
 	val = valSet.Validators[index]
 	return val.Address, val.Copy()
 }
 
-func (valSet *ValidatorSet) Size() uint {
-	return uint(len(valSet.Validators))
+func (valSet *ValidatorSet) Size() int {
+	return len(valSet.Validators)
 }
 
-func (valSet *ValidatorSet) TotalVotingPower() uint64 {
+func (valSet *ValidatorSet) TotalVotingPower() int64 {
 	if valSet.totalVotingPower == 0 {
 		for _, val := range valSet.Validators {
 			valSet.totalVotingPower += val.VotingPower
@@ -190,9 +190,9 @@ func (valSet *ValidatorSet) Remove(address []byte) (val *Validator, removed bool
 	}
 }
 
-func (valSet *ValidatorSet) Iterate(fn func(index uint, val *Validator) bool) {
+func (valSet *ValidatorSet) Iterate(fn func(index int, val *Validator) bool) {
 	for i, val := range valSet.Validators {
-		stop := fn(uint(i), val.Copy())
+		stop := fn(i, val.Copy())
 		if stop {
 			break
 		}
@@ -201,15 +201,15 @@ func (valSet *ValidatorSet) Iterate(fn func(index uint, val *Validator) bool) {
 
 // Verify that +2/3 of the set had signed the given signBytes
 func (valSet *ValidatorSet) VerifyValidation(chainID string,
-	hash []byte, parts types.PartSetHeader, height uint, v *types.Validation) error {
-	if valSet.Size() != uint(len(v.Precommits)) {
+	hash []byte, parts types.PartSetHeader, height int, v *types.Validation) error {
+	if valSet.Size() != len(v.Precommits) {
 		return fmt.Errorf("Invalid validation -- wrong set size: %v vs %v", valSet.Size(), len(v.Precommits))
 	}
 	if height != v.Height() {
 		return fmt.Errorf("Invalid validation -- wrong height: %v vs %v", height, v.Height())
 	}
 
-	talliedVotingPower := uint64(0)
+	talliedVotingPower := int64(0)
 	round := v.Round()
 
 	for idx, precommit := range v.Precommits {
@@ -226,7 +226,7 @@ func (valSet *ValidatorSet) VerifyValidation(chainID string,
 		if precommit.Type != types.VoteTypePrecommit {
 			return fmt.Errorf("Invalid validation -- not precommit @ index %v", idx)
 		}
-		_, val := valSet.GetByIndex(uint(idx))
+		_, val := valSet.GetByIndex(idx)
 		// Validate signature
 		precommitSignBytes := account.SignBytes(chainID, precommit)
 		if !val.PubKey.VerifyBytes(precommitSignBytes, precommit.Signature) {
@@ -256,7 +256,7 @@ func (valSet *ValidatorSet) String() string {
 
 func (valSet *ValidatorSet) StringIndented(indent string) string {
 	valStrings := []string{}
-	valSet.Iterate(func(index uint, val *Validator) bool {
+	valSet.Iterate(func(index int, val *Validator) bool {
 		valStrings = append(valStrings, val.String())
 		return false
 	})
@@ -294,9 +294,9 @@ func (vs ValidatorsByAddress) Swap(i, j int) {
 //-------------------------------------
 // Use with Heap for sorting validators by accum
 
-type accumComparable uint64
+type accumComparable int64
 
 // We want to find the validator with the greatest accum.
 func (ac accumComparable) Less(o interface{}) bool {
-	return uint64(ac) < uint64(o.(accumComparable))
+	return int64(ac) < int64(o.(accumComparable))
 }
diff --git a/state/validator_set_test.go b/state/validator_set_test.go
index be108acf..dc74d484 100644
--- a/state/validator_set_test.go
+++ b/state/validator_set_test.go
@@ -13,9 +13,9 @@ func randValidator_() *Validator {
 	return &Validator{
 		Address:     RandBytes(20),
 		PubKey:      account.PubKeyEd25519(RandBytes(64)),
-		BondHeight:  uint(RandUint32()),
-		VotingPower: RandUint64(),
-		Accum:       int64(RandUint64()),
+		BondHeight:  RandInt(),
+		VotingPower: RandInt64(),
+		Accum:       RandInt64(),
 	}
 }
 
diff --git a/types/block.go b/types/block.go
index b149c44e..2fdf9f1d 100644
--- a/types/block.go
+++ b/types/block.go
@@ -21,7 +21,7 @@ type Block struct {
 }
 
 // Basic validation that doesn't involve state data.
-func (b *Block) ValidateBasic(chainID string, lastBlockHeight uint, lastBlockHash []byte,
+func (b *Block) ValidateBasic(chainID string, lastBlockHeight int, lastBlockHash []byte,
 	lastBlockParts PartSetHeader, lastBlockTime time.Time) error {
 	if b.ChainID != chainID {
 		return errors.New("Wrong Block.Header.ChainID")
@@ -29,7 +29,7 @@ func (b *Block) ValidateBasic(chainID string, lastBlockHeight uint, lastBlockHas
 	if b.Height != lastBlockHeight+1 {
 		return errors.New("Wrong Block.Header.Height")
 	}
-	if b.NumTxs != uint(len(b.Data.Txs)) {
+	if b.NumTxs != len(b.Data.Txs) {
 		return errors.New("Wrong Block.Header.NumTxs")
 	}
 	if !bytes.Equal(b.LastBlockHash, lastBlockHash) {
@@ -123,10 +123,10 @@ func (b *Block) StringShort() string {
 
 type Header struct {
 	ChainID        string        `json:"chain_id"`
-	Height         uint          `json:"height"`
+	Height         int           `json:"height"`
 	Time           time.Time     `json:"time"`
-	Fees           uint64        `json:"fees"`
-	NumTxs         uint          `json:"num_txs"`
+	Fees           int64         `json:"fees"`
+	NumTxs         int           `json:"num_txs"`
 	LastBlockHash  []byte        `json:"last_block_hash"`
 	LastBlockParts PartSetHeader `json:"last_block_parts"`
 	StateHash      []byte        `json:"state_hash"`
@@ -188,14 +188,14 @@ type Validation struct {
 	bitArray *BitArray
 }
 
-func (v *Validation) Height() uint {
+func (v *Validation) Height() int {
 	if len(v.Precommits) == 0 {
 		return 0
 	}
 	return v.Precommits[0].Height
 }
 
-func (v *Validation) Round() uint {
+func (v *Validation) Round() int {
 	if len(v.Precommits) == 0 {
 		return 0
 	}
@@ -259,9 +259,9 @@ func (v *Validation) StringIndented(indent string) string {
 
 func (v *Validation) BitArray() *BitArray {
 	if v.bitArray == nil {
-		v.bitArray = NewBitArray(uint(len(v.Precommits)))
+		v.bitArray = NewBitArray(len(v.Precommits))
 		for i, precommit := range v.Precommits {
-			v.bitArray.SetIndex(uint(i), precommit != nil)
+			v.bitArray.SetIndex(i, precommit != nil)
 		}
 	}
 	return v.bitArray
diff --git a/types/events.go b/types/events.go
index e51d9e28..31cedf12 100644
--- a/types/events.go
+++ b/types/events.go
@@ -55,8 +55,8 @@ type CallData struct {
 	Caller []byte `json:"caller"`
 	Callee []byte `json:"callee"`
 	Data   []byte `json:"data"`
-	Value  uint64 `json:"value"`
-	Gas    uint64 `json:"gas"`
+	Value  int64  `json:"value"`
+	Gas    int64  `json:"gas"`
 }
 
 type EventMsgCall struct {
diff --git a/types/names.go b/types/names.go
index bebecb47..9ce4cc6f 100644
--- a/types/names.go
+++ b/types/names.go
@@ -5,12 +5,12 @@ import (
 )
 
 var (
-	MinNameRegistrationPeriod uint64 = 5
+	MinNameRegistrationPeriod int = 5
 
 	// cost for storing a name for a block is
 	// CostPerBlock*CostPerByte*(len(data) + 32)
-	NameCostPerByte  uint64 = 1
-	NameCostPerBlock uint64 = 1
+	NameCostPerByte  int64 = 1
+	NameCostPerBlock int64 = 1
 
 	MaxNameLength = 32
 	MaxDataLength = 1 << 16
@@ -31,15 +31,15 @@ func validateNameRegEntryData(data string) bool {
 }
 
 // base cost is "effective" number of bytes
-func BaseEntryCost(name, data string) uint64 {
-	return uint64(len(data) + 32)
+func BaseEntryCost(name, data string) int64 {
+	return int64(len(data) + 32)
 }
 
 type NameRegEntry struct {
 	Name    string `json:"name"`    // registered name for the entry
 	Owner   []byte `json:"owner"`   // address that created the entry
 	Data    string `json:"data"`    // data to store under this name
-	Expires uint64 `json:"expires"` // block at which this entry expires
+	Expires int    `json:"expires"` // block at which this entry expires
 }
 
 func (entry *NameRegEntry) Copy() *NameRegEntry {
diff --git a/types/part_set.go b/types/part_set.go
index 8c5de3be..8d4ba320 100644
--- a/types/part_set.go
+++ b/types/part_set.go
@@ -61,7 +61,7 @@ func (part *Part) StringIndented(indent string) string {
 //-------------------------------------
 
 type PartSetHeader struct {
-	Total uint   `json:"total"`
+	Total int    `json:"total"`
 	Hash  []byte `json:"hash"`
 }
 
@@ -84,13 +84,13 @@ func (psh PartSetHeader) WriteSignBytes(w io.Writer, n *int64, err *error) {
 //-------------------------------------
 
 type PartSet struct {
-	total uint
+	total int
 	hash  []byte
 
 	mtx           sync.Mutex
 	parts         []*Part
 	partsBitArray *BitArray
-	count         uint
+	count         int
 }
 
 // Returns an immutable, full PartSet from the data bytes.
@@ -100,14 +100,14 @@ func NewPartSetFromData(data []byte) *PartSet {
 	total := (len(data) + partSize - 1) / partSize
 	parts := make([]*Part, total)
 	parts_ := make([]merkle.Hashable, total)
-	partsBitArray := NewBitArray(uint(total))
+	partsBitArray := NewBitArray(total)
 	for i := 0; i < total; i++ {
 		part := &Part{
 			Bytes: data[i*partSize : MinInt(len(data), (i+1)*partSize)],
 		}
 		parts[i] = part
 		parts_[i] = part
-		partsBitArray.SetIndex(uint(i), true)
+		partsBitArray.SetIndex(i, true)
 	}
 	// Compute merkle proofs
 	proofs := merkle.SimpleProofsFromHashables(parts_)
@@ -115,11 +115,11 @@ func NewPartSetFromData(data []byte) *PartSet {
 		parts[i].Proof = *proofs[i]
 	}
 	return &PartSet{
-		total:         uint(total),
+		total:         total,
 		hash:          proofs[0].RootHash,
 		parts:         parts,
 		partsBitArray: partsBitArray,
-		count:         uint(total),
+		count:         total,
 	}
 }
 
@@ -129,7 +129,7 @@ func NewPartSetFromHeader(header PartSetHeader) *PartSet {
 		total:         header.Total,
 		hash:          header.Hash,
 		parts:         make([]*Part, header.Total),
-		partsBitArray: NewBitArray(uint(header.Total)),
+		partsBitArray: NewBitArray(header.Total),
 		count:         0,
 	}
 }
@@ -173,14 +173,14 @@ func (ps *PartSet) HashesTo(hash []byte) bool {
 	return bytes.Equal(ps.hash, hash)
 }
 
-func (ps *PartSet) Count() uint {
+func (ps *PartSet) Count() int {
 	if ps == nil {
 		return 0
 	}
 	return ps.count
 }
 
-func (ps *PartSet) Total() uint {
+func (ps *PartSet) Total() int {
 	if ps == nil {
 		return 0
 	}
@@ -208,12 +208,12 @@ func (ps *PartSet) AddPart(part *Part) (bool, error) {
 
 	// Add part
 	ps.parts[part.Proof.Index] = part
-	ps.partsBitArray.SetIndex(uint(part.Proof.Index), true)
+	ps.partsBitArray.SetIndex(part.Proof.Index, true)
 	ps.count++
 	return true, nil
 }
 
-func (ps *PartSet) GetPart(index uint) *Part {
+func (ps *PartSet) GetPart(index int) *Part {
 	ps.mtx.Lock()
 	defer ps.mtx.Unlock()
 	return ps.parts[index]
diff --git a/types/part_set_test.go b/types/part_set_test.go
index 88cf2d58..5d2d9142 100644
--- a/types/part_set_test.go
+++ b/types/part_set_test.go
@@ -27,7 +27,7 @@ func TestBasicPartSet(t *testing.T) {
 	// Test adding parts to a new partSet.
 	partSet2 := NewPartSetFromHeader(partSet.Header())
 
-	for i := uint(0); i < partSet.Total(); i++ {
+	for i := 0; i < partSet.Total(); i++ {
 		part := partSet.GetPart(i)
 		//t.Logf("\n%v", part)
 		added, err := partSet2.AddPart(part)
diff --git a/types/tx.go b/types/tx.go
index 46362413..690528bc 100644
--- a/types/tx.go
+++ b/types/tx.go
@@ -24,8 +24,8 @@ var (
 )
 
 type ErrTxInvalidSequence struct {
-	Got      uint64
-	Expected uint64
+	Got      int
+	Expected int
 }
 
 func (e ErrTxInvalidSequence) Error() string {
@@ -79,8 +79,8 @@ var _ = binary.RegisterInterface(
 
 type TxInput struct {
 	Address   []byte            `json:"address"`   // Hash of the PubKey
-	Amount    uint64            `json:"amount"`    // Must not exceed account balance
-	Sequence  uint              `json:"sequence"`  // Must be 1 greater than the last committed TxInput
+	Amount    int64             `json:"amount"`    // Must not exceed account balance
+	Sequence  int               `json:"sequence"`  // Must be 1 greater than the last committed TxInput
 	Signature account.Signature `json:"signature"` // Depends on the PubKey type and the whole Tx
 	PubKey    account.PubKey    `json:"pub_key"`   // Must not be nil, may be nil
 }
@@ -107,7 +107,7 @@ func (txIn *TxInput) String() string {
 
 type TxOutput struct {
 	Address []byte `json:"address"` // Hash of the PubKey
-	Amount  uint64 `json:"amount"`  // The sum of all outputs must not exceed the inputs.
+	Amount  int64  `json:"amount"`  // The sum of all outputs must not exceed the inputs.
 }
 
 func (txOut *TxOutput) ValidateBasic() error {
@@ -163,8 +163,8 @@ func (tx *SendTx) String() string {
 type CallTx struct {
 	Input    *TxInput `json:"input"`
 	Address  []byte   `json:"address"`
-	GasLimit uint64   `json:"gas_limit"`
-	Fee      uint64   `json:"fee"`
+	GasLimit int64    `json:"gas_limit"`
+	Fee      int64    `json:"fee"`
 	Data     []byte   `json:"data"`
 }
 
@@ -186,7 +186,7 @@ type NameTx struct {
 	Input *TxInput `json:"input"`
 	Name  string   `json:"name"`
 	Data  string   `json:"data"`
-	Fee   uint64   `json:"fee"`
+	Fee   int64    `json:"fee"`
 }
 
 func (tx *NameTx) WriteSignBytes(chainID string, w io.Writer, n *int64, err *error) {
@@ -220,7 +220,7 @@ func (tx *NameTx) ValidateStrings() error {
 	return nil
 }
 
-func (tx *NameTx) BaseEntryCost() uint64 {
+func (tx *NameTx) BaseEntryCost() int64 {
 	return BaseEntryCost(tx.Name, tx.Data)
 }
 
@@ -266,7 +266,7 @@ func (tx *BondTx) String() string {
 
 type UnbondTx struct {
 	Address   []byte                   `json:"address"`
-	Height    uint                     `json:"height"`
+	Height    int                      `json:"height"`
 	Signature account.SignatureEd25519 `json:"signature"`
 }
 
@@ -283,7 +283,7 @@ func (tx *UnbondTx) String() string {
 
 type RebondTx struct {
 	Address   []byte                   `json:"address"`
-	Height    uint                     `json:"height"`
+	Height    int                      `json:"height"`
 	Signature account.SignatureEd25519 `json:"signature"`
 }
 
diff --git a/types/tx_utils.go b/types/tx_utils.go
index a4ba02de..1a960b6a 100644
--- a/types/tx_utils.go
+++ b/types/tx_utils.go
@@ -19,7 +19,7 @@ func NewSendTx() *SendTx {
 	}
 }
 
-func (tx *SendTx) AddInput(st AccountGetter, pubkey account.PubKey, amt uint64) error {
+func (tx *SendTx) AddInput(st AccountGetter, pubkey account.PubKey, amt int64) error {
 	addr := pubkey.Address()
 	acc := st.GetAccount(addr)
 	if acc == nil {
@@ -28,7 +28,7 @@ func (tx *SendTx) AddInput(st AccountGetter, pubkey account.PubKey, amt uint64)
 	return tx.AddInputWithNonce(pubkey, amt, acc.Sequence+1)
 }
 
-func (tx *SendTx) AddInputWithNonce(pubkey account.PubKey, amt uint64, nonce uint) error {
+func (tx *SendTx) AddInputWithNonce(pubkey account.PubKey, amt int64, nonce int) error {
 	addr := pubkey.Address()
 	tx.Inputs = append(tx.Inputs, &TxInput{
 		Address:   addr,
@@ -40,7 +40,7 @@ func (tx *SendTx) AddInputWithNonce(pubkey account.PubKey, amt uint64, nonce uin
 	return nil
 }
 
-func (tx *SendTx) AddOutput(addr []byte, amt uint64) error {
+func (tx *SendTx) AddOutput(addr []byte, amt int64) error {
 	tx.Outputs = append(tx.Outputs, &TxOutput{
 		Address: addr,
 		Amount:  amt,
@@ -60,7 +60,7 @@ func (tx *SendTx) SignInput(chainID string, i int, privAccount *account.PrivAcco
 //----------------------------------------------------------------------------
 // CallTx interface for creating tx
 
-func NewCallTx(st AccountGetter, from account.PubKey, to, data []byte, amt, gasLimit, fee uint64) (*CallTx, error) {
+func NewCallTx(st AccountGetter, from account.PubKey, to, data []byte, amt, gasLimit, fee int64) (*CallTx, error) {
 	addr := from.Address()
 	acc := st.GetAccount(addr)
 	if acc == nil {
@@ -71,7 +71,7 @@ func NewCallTx(st AccountGetter, from account.PubKey, to, data []byte, amt, gasL
 	return NewCallTxWithNonce(from, to, data, amt, gasLimit, fee, nonce), nil
 }
 
-func NewCallTxWithNonce(from account.PubKey, to, data []byte, amt, gasLimit, fee uint64, nonce uint) *CallTx {
+func NewCallTxWithNonce(from account.PubKey, to, data []byte, amt, gasLimit, fee int64, nonce int) *CallTx {
 	addr := from.Address()
 	input := &TxInput{
 		Address:   addr,
@@ -98,7 +98,7 @@ func (tx *CallTx) Sign(chainID string, privAccount *account.PrivAccount) {
 //----------------------------------------------------------------------------
 // NameTx interface for creating tx
 
-func NewNameTx(st AccountGetter, from account.PubKey, name, data string, amt, fee uint64) (*NameTx, error) {
+func NewNameTx(st AccountGetter, from account.PubKey, name, data string, amt, fee int64) (*NameTx, error) {
 	addr := from.Address()
 	acc := st.GetAccount(addr)
 	if acc == nil {
@@ -109,7 +109,7 @@ func NewNameTx(st AccountGetter, from account.PubKey, name, data string, amt, fe
 	return NewNameTxWithNonce(from, name, data, amt, fee, nonce), nil
 }
 
-func NewNameTxWithNonce(from account.PubKey, name, data string, amt, fee uint64, nonce uint) *NameTx {
+func NewNameTxWithNonce(from account.PubKey, name, data string, amt, fee int64, nonce int) *NameTx {
 	addr := from.Address()
 	input := &TxInput{
 		Address:   addr,
@@ -147,7 +147,7 @@ func NewBondTx(pubkey account.PubKey) (*BondTx, error) {
 	}, nil
 }
 
-func (tx *BondTx) AddInput(st AccountGetter, pubkey account.PubKey, amt uint64) error {
+func (tx *BondTx) AddInput(st AccountGetter, pubkey account.PubKey, amt int64) error {
 	addr := pubkey.Address()
 	acc := st.GetAccount(addr)
 	if acc == nil {
@@ -156,7 +156,7 @@ func (tx *BondTx) AddInput(st AccountGetter, pubkey account.PubKey, amt uint64)
 	return tx.AddInputWithNonce(pubkey, amt, acc.Sequence+1)
 }
 
-func (tx *BondTx) AddInputWithNonce(pubkey account.PubKey, amt uint64, nonce uint) error {
+func (tx *BondTx) AddInputWithNonce(pubkey account.PubKey, amt int64, nonce int) error {
 	addr := pubkey.Address()
 	tx.Inputs = append(tx.Inputs, &TxInput{
 		Address:   addr,
@@ -168,7 +168,7 @@ func (tx *BondTx) AddInputWithNonce(pubkey account.PubKey, amt uint64, nonce uin
 	return nil
 }
 
-func (tx *BondTx) AddOutput(addr []byte, amt uint64) error {
+func (tx *BondTx) AddOutput(addr []byte, amt int64) error {
 	tx.UnbondTo = append(tx.UnbondTo, &TxOutput{
 		Address: addr,
 		Amount:  amt,
@@ -198,7 +198,7 @@ func (tx *BondTx) SignInput(chainID string, i int, privAccount *account.PrivAcco
 //----------------------------------------------------------------------
 // UnbondTx interface for creating tx
 
-func NewUnbondTx(addr []byte, height uint) *UnbondTx {
+func NewUnbondTx(addr []byte, height int) *UnbondTx {
 	return &UnbondTx{
 		Address: addr,
 		Height:  height,
@@ -212,7 +212,7 @@ func (tx *UnbondTx) Sign(chainID string, privAccount *account.PrivAccount) {
 //----------------------------------------------------------------------
 // RebondTx interface for creating tx
 
-func NewRebondTx(addr []byte, height uint) *RebondTx {
+func NewRebondTx(addr []byte, height int) *RebondTx {
 	return &RebondTx{
 		Address: addr,
 		Height:  height,
diff --git a/types/vote.go b/types/vote.go
index 2e931c23..30205d88 100644
--- a/types/vote.go
+++ b/types/vote.go
@@ -28,8 +28,8 @@ func (err *ErrVoteConflictingSignature) Error() string {
 
 // Represents a prevote, precommit, or commit vote from validators for consensus.
 type Vote struct {
-	Height     uint                     `json:"height"`
-	Round      uint                     `json:"round"`
+	Height     int                      `json:"height"`
+	Round      int                      `json:"round"`
 	Type       byte                     `json:"type"`
 	BlockHash  []byte                   `json:"block_hash"`  // empty if vote is nil.
 	BlockParts PartSetHeader            `json:"block_parts"` // zero if vote is nil.
diff --git a/vm/gas.go b/vm/gas.go
index ebe5573a..dac978f1 100644
--- a/vm/gas.go
+++ b/vm/gas.go
@@ -1,17 +1,17 @@
 package vm
 
 const (
-	GasSha3          uint64 = 1
-	GasGetAccount    uint64 = 1
-	GasStorageUpdate uint64 = 1
+	GasSha3          int64 = 1
+	GasGetAccount    int64 = 1
+	GasStorageUpdate int64 = 1
 
-	GasStackOp uint64 = 1
+	GasStackOp int64 = 1
 
-	GasEcRecover     uint64 = 1
-	GasSha256Word    uint64 = 1
-	GasSha256Base    uint64 = 1
-	GasRipemd160Word uint64 = 1
-	GasRipemd160Base uint64 = 1
-	GasIdentityWord  uint64 = 1
-	GasIdentityBase  uint64 = 1
+	GasEcRecover     int64 = 1
+	GasSha256Word    int64 = 1
+	GasSha256Base    int64 = 1
+	GasRipemd160Word int64 = 1
+	GasRipemd160Base int64 = 1
+	GasIdentityWord  int64 = 1
+	GasIdentityBase  int64 = 1
 )
diff --git a/vm/native.go b/vm/native.go
index 8aff146d..b7339bc3 100644
--- a/vm/native.go
+++ b/vm/native.go
@@ -11,17 +11,17 @@ import (
 var nativeContracts = make(map[Word256]NativeContract)
 
 func init() {
-	nativeContracts[Uint64ToWord256(1)] = ecrecoverFunc
-	nativeContracts[Uint64ToWord256(2)] = sha256Func
-	nativeContracts[Uint64ToWord256(3)] = ripemd160Func
-	nativeContracts[Uint64ToWord256(4)] = identityFunc
+	nativeContracts[Int64ToWord256(1)] = ecrecoverFunc
+	nativeContracts[Int64ToWord256(2)] = sha256Func
+	nativeContracts[Int64ToWord256(3)] = ripemd160Func
+	nativeContracts[Int64ToWord256(4)] = identityFunc
 }
 
 //-----------------------------------------------------------------------------
 
-type NativeContract func(input []byte, gas *uint64) (output []byte, err error)
+type NativeContract func(input []byte, gas *int64) (output []byte, err error)
 
-func ecrecoverFunc(input []byte, gas *uint64) (output []byte, err error) {
+func ecrecoverFunc(input []byte, gas *int64) (output []byte, err error) {
 	// Deduct gas
 	gasRequired := GasEcRecover
 	if *gas < gasRequired {
@@ -42,9 +42,9 @@ func ecrecoverFunc(input []byte, gas *uint64) (output []byte, err error) {
 	return LeftPadBytes(hashed, 32), nil
 }
 
-func sha256Func(input []byte, gas *uint64) (output []byte, err error) {
+func sha256Func(input []byte, gas *int64) (output []byte, err error) {
 	// Deduct gas
-	gasRequired := uint64((len(input)+31)/32)*GasSha256Word + GasSha256Base
+	gasRequired := int64((len(input)+31)/32)*GasSha256Word + GasSha256Base
 	if *gas < gasRequired {
 		return nil, ErrInsufficientGas
 	} else {
@@ -59,9 +59,9 @@ func sha256Func(input []byte, gas *uint64) (output []byte, err error) {
 	return hasher.Sum(nil), nil
 }
 
-func ripemd160Func(input []byte, gas *uint64) (output []byte, err error) {
+func ripemd160Func(input []byte, gas *int64) (output []byte, err error) {
 	// Deduct gas
-	gasRequired := uint64((len(input)+31)/32)*GasRipemd160Word + GasRipemd160Base
+	gasRequired := int64((len(input)+31)/32)*GasRipemd160Word + GasRipemd160Base
 	if *gas < gasRequired {
 		return nil, ErrInsufficientGas
 	} else {
@@ -76,9 +76,9 @@ func ripemd160Func(input []byte, gas *uint64) (output []byte, err error) {
 	return LeftPadBytes(hasher.Sum(nil), 32), nil
 }
 
-func identityFunc(input []byte, gas *uint64) (output []byte, err error) {
+func identityFunc(input []byte, gas *int64) (output []byte, err error) {
 	// Deduct gas
-	gasRequired := uint64((len(input)+31)/32)*GasIdentityWord + GasIdentityBase
+	gasRequired := int64((len(input)+31)/32)*GasIdentityWord + GasIdentityBase
 	if *gas < gasRequired {
 		return nil, ErrInsufficientGas
 	} else {
diff --git a/vm/stack.go b/vm/stack.go
index 500ff4d1..12bc1b77 100644
--- a/vm/stack.go
+++ b/vm/stack.go
@@ -10,11 +10,11 @@ type Stack struct {
 	data []Word256
 	ptr  int
 
-	gas *uint64
+	gas *int64
 	err *error
 }
 
-func NewStack(capacity int, gas *uint64, err *error) *Stack {
+func NewStack(capacity int, gas *int64, err *error) *Stack {
 	return &Stack{
 		data: make([]Word256, capacity),
 		ptr:  0,
@@ -23,7 +23,7 @@ func NewStack(capacity int, gas *uint64, err *error) *Stack {
 	}
 }
 
-func (st *Stack) useGas(gasToUse uint64) {
+func (st *Stack) useGas(gasToUse int64) {
 	if *st.gas > gasToUse {
 		*st.gas -= gasToUse
 	} else {
@@ -54,8 +54,8 @@ func (st *Stack) PushBytes(bz []byte) {
 	st.Push(LeftPadWord256(bz))
 }
 
-func (st *Stack) Push64(i uint64) {
-	st.Push(Uint64ToWord256(i))
+func (st *Stack) Push64(i int64) {
+	st.Push(Int64ToWord256(i))
 }
 
 func (st *Stack) Pop() Word256 {
@@ -72,9 +72,9 @@ func (st *Stack) PopBytes() []byte {
 	return st.Pop().Bytes()
 }
 
-func (st *Stack) Pop64() uint64 {
+func (st *Stack) Pop64() int64 {
 	d := st.Pop()
-	return Uint64FromWord256(d)
+	return Int64FromWord256(d)
 }
 
 func (st *Stack) Len() int {
diff --git a/vm/test/fake_app_state.go b/vm/test/fake_app_state.go
index 6f703d72..4880814b 100644
--- a/vm/test/fake_app_state.go
+++ b/vm/test/fake_app_state.go
@@ -80,6 +80,6 @@ func createAddress(creator *Account) Word256 {
 	creator.Nonce += 1
 	temp := make([]byte, 32+8)
 	copy(temp, creator.Address[:])
-	PutUint64BE(temp[32:], nonce)
+	PutInt64BE(temp[32:], nonce)
 	return LeftPadWord256(sha3.Sha3(temp)[:20])
 }
diff --git a/vm/test/vm_test.go b/vm/test/vm_test.go
index e285a911..716643c4 100644
--- a/vm/test/vm_test.go
+++ b/vm/test/vm_test.go
@@ -43,13 +43,13 @@ func TestVM(t *testing.T) {
 
 	// Create accounts
 	account1 := &Account{
-		Address: Uint64ToWord256(100),
+		Address: Int64ToWord256(100),
 	}
 	account2 := &Account{
-		Address: Uint64ToWord256(101),
+		Address: Int64ToWord256(101),
 	}
 
-	var gas uint64 = 100000
+	var gas int64 = 100000
 	N := []byte{0x0f, 0x0f}
 	// Loop N times
 	code := []byte{0x60, 0x00, 0x60, 0x20, 0x52, 0x5B, byte(0x60 + len(N) - 1)}
@@ -81,7 +81,7 @@ func TestSubcurrency(t *testing.T) {
 
 	ourVm := NewVM(st, newParams(), Zero256, nil)
 
-	var gas uint64 = 1000
+	var gas int64 = 1000
 	code_parts := []string{"620f42403355",
 		"7c0100000000000000000000000000000000000000000000000000000000",
 		"600035046315cf268481141561004657",
@@ -105,13 +105,13 @@ func TestSendCall(t *testing.T) {
 
 	// Create accounts
 	account1 := &Account{
-		Address: Uint64ToWord256(100),
+		Address: Int64ToWord256(100),
 	}
 	account2 := &Account{
-		Address: Uint64ToWord256(101),
+		Address: Int64ToWord256(101),
 	}
 	account3 := &Account{
-		Address: Uint64ToWord256(102),
+		Address: Int64ToWord256(102),
 	}
 
 	// account1 will call account2 which will trigger CALL opcode to account3
@@ -146,7 +146,7 @@ func TestSendCall(t *testing.T) {
 }
 
 // subscribes to an AccReceive, runs the vm, returns the exception
-func runVMWaitEvents(t *testing.T, ourVm *VM, caller, callee *Account, subscribeAddr, contractCode []byte, gas uint64) string {
+func runVMWaitEvents(t *testing.T, ourVm *VM, caller, callee *Account, subscribeAddr, contractCode []byte, gas int64) string {
 	// we need to catch the event from the CALL to check for exceptions
 	evsw := new(events.EventSwitch)
 	evsw.Start()
diff --git a/vm/types.go b/vm/types.go
index d5777213..fe872c83 100644
--- a/vm/types.go
+++ b/vm/types.go
@@ -10,9 +10,9 @@ const (
 
 type Account struct {
 	Address     Word256
-	Balance     uint64
+	Balance     int64
 	Code        []byte
-	Nonce       uint64
+	Nonce       int64
 	StorageRoot Word256
 	Other       interface{} // For holding all other data.
 }
@@ -26,7 +26,7 @@ type Log struct {
 	Address Word256
 	Topics  []Word256
 	Data    []byte
-	Height  uint64
+	Height  int64
 }
 
 type AppState interface {
@@ -46,8 +46,8 @@ type AppState interface {
 }
 
 type Params struct {
-	BlockHeight uint64
+	BlockHeight int64
 	BlockHash   Word256
 	BlockTime   int64
-	GasLimit    uint64
+	GasLimit    int64
 }
diff --git a/vm/vm.go b/vm/vm.go
index 6a814655..dc58f950 100644
--- a/vm/vm.go
+++ b/vm/vm.go
@@ -72,7 +72,7 @@ func (vm *VM) SetFireable(evc events.Fireable) {
 // value: To be transferred from caller to callee. Refunded upon error.
 // gas:   Available gas. No refunds for gas.
 // code: May be nil, since the CALL opcode may be used to send value from contracts to accounts
-func (vm *VM) Call(caller, callee *Account, code, input []byte, value uint64, gas *uint64) (output []byte, err error) {
+func (vm *VM) Call(caller, callee *Account, code, input []byte, value int64, gas *int64) (output []byte, err error) {
 
 	exception := new(string)
 	defer func() {
@@ -109,14 +109,14 @@ func (vm *VM) Call(caller, callee *Account, code, input []byte, value uint64, ga
 }
 
 // Just like Call() but does not transfer 'value' or modify the callDepth.
-func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, gas *uint64) (output []byte, err error) {
+func (vm *VM) call(caller, callee *Account, code, input []byte, value int64, gas *int64) (output []byte, err error) {
 	dbg.Printf("(%d) (%X) %X (code=%d) gas: %v (d) %X\n", vm.callDepth, caller.Address[:4], callee.Address, len(callee.Code), *gas, input)
 
 	var (
-		pc     uint64 = 0
-		stack         = NewStack(dataStackCapacity, gas, &err)
-		memory        = make([]byte, memoryCapacity)
-		ok            = false // convenience
+		pc     int64 = 0
+		stack        = NewStack(dataStackCapacity, gas, &err)
+		memory       = make([]byte, memoryCapacity)
+		ok           = false // convenience
 	)
 
 	for {
@@ -388,7 +388,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 			if idx < 32 {
 				res = val[idx]
 			}
-			stack.Push64(uint64(res))
+			stack.Push64(int64(res))
 			dbg.Printf(" => 0x%X\n", res)
 
 		case SHA3: // 0x20
@@ -444,7 +444,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 			dbg.Printf(" => 0x%X\n", res)
 
 		case CALLDATASIZE: // 0x36
-			stack.Push64(uint64(len(input)))
+			stack.Push64(int64(len(input)))
 			dbg.Printf(" => %d\n", len(input))
 
 		case CALLDATACOPY: // 0x37
@@ -463,7 +463,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 			dbg.Printf(" => [%v, %v, %v] %X\n", memOff, inputOff, length, data)
 
 		case CODESIZE: // 0x38
-			l := uint64(len(code))
+			l := int64(len(code))
 			stack.Push64(l)
 			dbg.Printf(" => %d\n", l)
 
@@ -496,7 +496,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 				return nil, firstErr(err, ErrUnknownAddress)
 			}
 			code := acc.Code
-			l := uint64(len(code))
+			l := int64(len(code))
 			stack.Push64(l)
 			dbg.Printf(" => %d\n", l)
 
@@ -534,11 +534,11 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 
 		case TIMESTAMP: // 0x42
 			time := vm.params.BlockTime
-			stack.Push64(uint64(time))
+			stack.Push64(int64(time))
 			dbg.Printf(" => 0x%X\n", time)
 
 		case BLOCKHEIGHT: // 0x43
-			number := uint64(vm.params.BlockHeight)
+			number := int64(vm.params.BlockHeight)
 			stack.Push64(number)
 			dbg.Printf(" => 0x%X\n", number)
 
@@ -604,7 +604,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 			stack.Push64(pc)
 
 		case MSIZE: // 0x59
-			stack.Push64(uint64(len(memory)))
+			stack.Push64(int64(len(memory)))
 
 		case GAS: // 0x5A
 			stack.Push64(*gas)
@@ -615,7 +615,7 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 			// Do nothing
 
 		case PUSH1, PUSH2, PUSH3, PUSH4, PUSH5, PUSH6, PUSH7, PUSH8, PUSH9, PUSH10, PUSH11, PUSH12, PUSH13, PUSH14, PUSH15, PUSH16, PUSH17, PUSH18, PUSH19, PUSH20, PUSH21, PUSH22, PUSH23, PUSH24, PUSH25, PUSH26, PUSH27, PUSH28, PUSH29, PUSH30, PUSH31, PUSH32:
-			a := uint64(op - PUSH1 + 1)
+			a := int64(op - PUSH1 + 1)
 			codeSegment, ok := subslice(code, pc+1, a)
 			if !ok {
 				return nil, firstErr(err, ErrCodeOutOfBounds)
@@ -792,8 +792,8 @@ func (vm *VM) call(caller, callee *Account, code, input []byte, value uint64, ga
 	}
 }
 
-func subslice(data []byte, offset, length uint64) (ret []byte, ok bool) {
-	size := uint64(len(data))
+func subslice(data []byte, offset, length int64) (ret []byte, ok bool) {
+	size := int64(len(data))
 	if size < offset {
 		return nil, false
 	} else if size < offset+length {
@@ -812,15 +812,15 @@ func rightMostBytes(data []byte, n int) []byte {
 	return data[offset:]
 }
 
-func codeGetOp(code []byte, n uint64) OpCode {
-	if uint64(len(code)) <= n {
+func codeGetOp(code []byte, n int64) OpCode {
+	if int64(len(code)) <= n {
 		return OpCode(0) // stop
 	} else {
 		return OpCode(code[n])
 	}
 }
 
-func jump(code []byte, to uint64, pc *uint64) (err error) {
+func jump(code []byte, to int64, pc *int64) (err error) {
 	dest := codeGetOp(code, to)
 	if dest != JUMPDEST {
 		dbg.Printf(" ~> %v invalid jump dest %v\n", to, dest)
@@ -839,7 +839,7 @@ func firstErr(errA, errB error) error {
 	}
 }
 
-func useGas(gas *uint64, gasToUse uint64) bool {
+func useGas(gas *int64, gasToUse int64) bool {
 	if *gas > gasToUse {
 		*gas -= gasToUse
 		return true
@@ -848,7 +848,7 @@ func useGas(gas *uint64, gasToUse uint64) bool {
 	}
 }
 
-func transfer(from, to *Account, amount uint64) error {
+func transfer(from, to *Account, amount int64) error {
 	if from.Balance < amount {
 		return ErrInsufficientBalance
 	} else {