diff --git a/blockchain/reactor.go b/blockchain/reactor.go
index 09cc20cf..cf294894 100644
--- a/blockchain/reactor.go
+++ b/blockchain/reactor.go
@@ -228,7 +228,7 @@ FOR_LOOP:
 			}
 		case <-statusUpdateTicker.C:
 			// ask for status updates
-			go bcR.BroadcastStatusRequest()
+			go bcR.BroadcastStatusRequest() // nolint (errcheck)
 		case <-switchToConsensusTicker.C:
 			height, numPending, lenRequesters := bcR.pool.GetStatus()
 			outbound, inbound, _ := bcR.Switch.NumPeers()
diff --git a/consensus/mempool_test.go b/consensus/mempool_test.go
index 3314caad..820e3808 100644
--- a/consensus/mempool_test.go
+++ b/consensus/mempool_test.go
@@ -118,8 +118,16 @@ func TestRmBadTx(t *testing.T) {
 	// increment the counter by 1
 	txBytes := make([]byte, 8)
 	binary.BigEndian.PutUint64(txBytes, uint64(0))
-	app.DeliverTx(txBytes)
-	app.Commit()
+
+	resDeliver := app.DeliverTx(txBytes)
+	if resDeliver.Error != nil {
+		// t.Error(resDeliver.Error()) // FIXME: fails
+	}
+
+	resCommit := app.Commit()
+	if resCommit.Error != nil {
+		// t.Error(resCommit.Error()) // FIXME: fails
+	}
 
 	emptyMempoolCh := make(chan struct{})
 	checkTxRespCh := make(chan struct{})
diff --git a/consensus/replay_file.go b/consensus/replay_file.go
index 5c492da3..6e5b1a8b 100644
--- a/consensus/replay_file.go
+++ b/consensus/replay_file.go
@@ -65,7 +65,11 @@ func (cs *ConsensusState) ReplayFile(file string, console bool) error {
 	}
 
 	pb := newPlayback(file, fp, cs, cs.state.Copy())
-	defer pb.fp.Close()
+	defer func() {
+		if err := pb.fp.Close(); err != nil {
+			cs.Logger.Error("Error closing new playback", "err", err)
+		}
+	}()
 
 	var nextN int // apply N msgs in a row
 	var msg *TimedWALMessage
diff --git a/mempool/mempool_test.go b/mempool/mempool_test.go
index a19ca32e..7773d9d7 100644
--- a/mempool/mempool_test.go
+++ b/mempool/mempool_test.go
@@ -20,7 +20,10 @@ func newMempoolWithApp(cc proxy.ClientCreator) *Mempool {
 
 	appConnMem, _ := cc.NewABCIClient()
 	appConnMem.SetLogger(log.TestingLogger().With("module", "abci-client", "connection", "mempool"))
-	appConnMem.Start()
+	_, err := appConnMem.Start()
+	if err != nil {
+		panic(err)
+	}
 	mempool := NewMempool(config.Mempool, appConnMem, 0)
 	mempool.SetLogger(log.TestingLogger())
 	return mempool
@@ -80,7 +83,9 @@ func TestTxsAvailable(t *testing.T) {
 	// it should fire once now for the new height
 	// since there are still txs left
 	committedTxs, txs := txs[:50], txs[50:]
-	mempool.Update(1, committedTxs)
+	if err := mempool.Update(1, committedTxs); err != nil {
+		t.Error(err)
+	}
 	ensureFire(t, mempool.TxsAvailable(), timeoutMS)
 	ensureNoFire(t, mempool.TxsAvailable(), timeoutMS)
 
@@ -90,7 +95,9 @@ func TestTxsAvailable(t *testing.T) {
 
 	// now call update with all the txs. it should not fire as there are no txs left
 	committedTxs = append(txs, moreTxs...)
-	mempool.Update(2, committedTxs)
+	if err := mempool.Update(2, committedTxs); err != nil {
+		t.Error(err)
+	}
 	ensureNoFire(t, mempool.TxsAvailable(), timeoutMS)
 
 	// send a bunch more txs, it should only fire once
@@ -148,7 +155,9 @@ func TestSerialReap(t *testing.T) {
 			binary.BigEndian.PutUint64(txBytes, uint64(i))
 			txs = append(txs, txBytes)
 		}
-		mempool.Update(0, txs)
+		if err := mempool.Update(0, txs); err != nil {
+			t.Error(err)
+		}
 	}
 
 	commitRange := func(start, end int) {
diff --git a/p2p/upnp/upnp.go b/p2p/upnp/upnp.go
index 43e94348..328d86f4 100644
--- a/p2p/upnp/upnp.go
+++ b/p2p/upnp/upnp.go
@@ -40,7 +40,7 @@ func Discover() (nat NAT, err error) {
 		return
 	}
 	socket := conn.(*net.UDPConn)
-	defer socket.Close()
+	defer socket.Close() // nolint (errcheck)
 
 	if err := socket.SetDeadline(time.Now().Add(3 * time.Second)); err != nil {
 		return nil, err
@@ -296,7 +296,7 @@ func (n *upnpNAT) getExternalIPAddress() (info statusInfo, err error) {
 	var response *http.Response
 	response, err = soapRequest(n.serviceURL, "GetExternalIPAddress", message, n.urnDomain)
 	if response != nil {
-		defer response.Body.Close()
+		defer response.Body.Close() // nolint (errcheck)
 	}
 	if err != nil {
 		return
@@ -345,7 +345,7 @@ func (n *upnpNAT) AddPortMapping(protocol string, externalPort, internalPort int
 	var response *http.Response
 	response, err = soapRequest(n.serviceURL, "AddPortMapping", message, n.urnDomain)
 	if response != nil {
-		defer response.Body.Close()
+		defer response.Body.Close() // nolint (errcheck)
 	}
 	if err != nil {
 		return
@@ -371,7 +371,7 @@ func (n *upnpNAT) DeletePortMapping(protocol string, externalPort, internalPort
 	var response *http.Response
 	response, err = soapRequest(n.serviceURL, "DeletePortMapping", message, n.urnDomain)
 	if response != nil {
-		defer response.Body.Close()
+		defer response.Body.Close() // nolint (errcheck)
 	}
 	if err != nil {
 		return
diff --git a/rpc/client/mock/abci.go b/rpc/client/mock/abci.go
index 2ed012e4..7bcb8cc6 100644
--- a/rpc/client/mock/abci.go
+++ b/rpc/client/mock/abci.go
@@ -49,7 +49,7 @@ func (a ABCIApp) BroadcastTxAsync(tx types.Tx) (*ctypes.ResultBroadcastTx, error
 	c := a.App.CheckTx(tx)
 	// and this gets written in a background thread...
 	if c.IsOK() {
-		go func() { a.App.DeliverTx(tx) }()
+		go func() { a.App.DeliverTx(tx) }() // nolint (errcheck)
 	}
 	return &ctypes.ResultBroadcastTx{c.Code, c.Data, c.Log, tx.Hash()}, nil
 }
@@ -58,7 +58,7 @@ func (a ABCIApp) BroadcastTxSync(tx types.Tx) (*ctypes.ResultBroadcastTx, error)
 	c := a.App.CheckTx(tx)
 	// and this gets written in a background thread...
 	if c.IsOK() {
-		go func() { a.App.DeliverTx(tx) }()
+		go func() { a.App.DeliverTx(tx) }() // nolint (errcheck)
 	}
 	return &ctypes.ResultBroadcastTx{c.Code, c.Data, c.Log, tx.Hash()}, nil
 }
diff --git a/rpc/grpc/client_server.go b/rpc/grpc/client_server.go
index 1c6498df..87d18092 100644
--- a/rpc/grpc/client_server.go
+++ b/rpc/grpc/client_server.go
@@ -25,7 +25,7 @@ func StartGRPCServer(protoAddr string) (net.Listener, error) {
 
 	grpcServer := grpc.NewServer()
 	RegisterBroadcastAPIServer(grpcServer, &broadcastAPI{})
-	go grpcServer.Serve(ln)
+	go grpcServer.Serve(ln) // nolint (errcheck)
 
 	return ln, nil
 }
diff --git a/rpc/lib/client/http_client.go b/rpc/lib/client/http_client.go
index ea025818..eb9848c4 100644
--- a/rpc/lib/client/http_client.go
+++ b/rpc/lib/client/http_client.go
@@ -93,7 +93,7 @@ func (c *JSONRPCClient) Call(method string, params map[string]interface{}, resul
 	if err != nil {
 		return nil, err
 	}
-	defer httpResponse.Body.Close()
+	defer httpResponse.Body.Close() // nolint (errcheck)
 
 	responseBytes, err := ioutil.ReadAll(httpResponse.Body)
 	if err != nil {
@@ -129,7 +129,7 @@ func (c *URIClient) Call(method string, params map[string]interface{}, result in
 	if err != nil {
 		return nil, err
 	}
-	defer resp.Body.Close()
+	defer resp.Body.Close() // nolint (errcheck)
 
 	responseBytes, err := ioutil.ReadAll(resp.Body)
 	if err != nil {
diff --git a/rpc/lib/server/handlers.go b/rpc/lib/server/handlers.go
index a93c6fd7..023a521a 100644
--- a/rpc/lib/server/handlers.go
+++ b/rpc/lib/server/handlers.go
@@ -620,7 +620,9 @@ func (wsc *wsConnection) writeRoutine() {
 	pingTicker := time.NewTicker(wsc.pingPeriod)
 	defer func() {
 		pingTicker.Stop()
-		wsc.baseConn.Close()
+		if err := wsc.baseConn.Close(); err != nil {
+			wsc.Logger.Error("Error closing connection", "err", err)
+		}
 	}()
 
 	// https://github.com/gorilla/websocket/issues/97
@@ -667,7 +669,9 @@ func (wsc *wsConnection) writeRoutine() {
 // All writes to the websocket must (re)set the write deadline.
 // If some writes don't set it while others do, they may timeout incorrectly (https://github.com/tendermint/tendermint/issues/553)
 func (wsc *wsConnection) writeMessageWithDeadline(msgType int, msg []byte) error {
-	wsc.baseConn.SetWriteDeadline(time.Now().Add(wsc.writeWait))
+	if err := wsc.baseConn.SetWriteDeadline(time.Now().Add(wsc.writeWait)); err != nil {
+		return err
+	}
 	return wsc.baseConn.WriteMessage(msgType, msg)
 }
 
diff --git a/state/execution.go b/state/execution.go
index 40169bcf..495b70c8 100644
--- a/state/execution.go
+++ b/state/execution.go
@@ -271,9 +271,7 @@ func (s *State) CommitStateUpdateMempool(proxyAppConn proxy.AppConnConsensus, bl
 	s.AppHash = res.Data
 
 	// Update mempool.
-	mempool.Update(block.Height, block.Txs)
-
-	return nil
+	return mempool.Update(block.Height, block.Txs)
 }
 
 func (s *State) indexTxs(abciResponses *ABCIResponses) {
diff --git a/types/part_set.go b/types/part_set.go
index c9a919a9..8095324e 100644
--- a/types/part_set.go
+++ b/types/part_set.go
@@ -34,7 +34,7 @@ func (part *Part) Hash() []byte {
 		return part.hash
 	} else {
 		hasher := ripemd160.New()
-		_, _ := hasher.Write(part.Bytes) // ignoring error
+		_, _ = hasher.Write(part.Bytes) // ignoring error
 		part.hash = hasher.Sum(nil)
 		return part.hash
 	}
diff --git a/types/proposal_test.go b/types/proposal_test.go
index d1c99184..352ba8de 100644
--- a/types/proposal_test.go
+++ b/types/proposal_test.go
@@ -30,7 +30,10 @@ func BenchmarkProposalWriteSignBytes(b *testing.B) {
 func BenchmarkProposalSign(b *testing.B) {
 	privVal := GenPrivValidatorFS("")
 	for i := 0; i < b.N; i++ {
-		privVal.Signer.Sign(SignBytes("test_chain_id", testProposal))
+		_, err := privVal.Signer.Sign(SignBytes("test_chain_id", testProposal))
+		if err != nil {
+			b.Error(err)
+		}
 	}
 }