diff --git a/client/client.go b/client/client.go
index b550dc92..5878b619 100644
--- a/client/client.go
+++ b/client/client.go
@@ -27,10 +27,10 @@ type Client interface {
 	EchoSync(msg string) (*types.ResponseEcho, error)
 	InfoSync(types.RequestInfo) (*types.ResponseInfo, error)
 	SetOptionSync(key string, value string) (log string, err error)
-	DeliverTxSync(tx []byte) *types.ResponseDeliverTx
-	CheckTxSync(tx []byte) *types.ResponseCheckTx
+	DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error)
+	CheckTxSync(tx []byte) (*types.ResponseCheckTx, error)
 	QuerySync(types.RequestQuery) (*types.ResponseQuery, error)
-	CommitSync() *types.ResponseCommit
+	CommitSync() (*types.ResponseCommit, error)
 
 	InitChainAsync(types.RequestInitChain) *ReqRes
 	BeginBlockAsync(types.RequestBeginBlock) *ReqRes
diff --git a/client/grpc_client.go b/client/grpc_client.go
index c7a4c2ae..6a53cb21 100644
--- a/client/grpc_client.go
+++ b/client/grpc_client.go
@@ -6,6 +6,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/pkg/errors"
 	context "golang.org/x/net/context"
 	grpc "google.golang.org/grpc"
 
@@ -267,20 +268,20 @@ func (cli *grpcClient) SetOptionSync(key string, value string) (log string, err
 	return reqres.Response.GetSetOption().Log, nil
 }
 
-func (cli *grpcClient) DeliverTxSync(tx []byte) *types.ResponseDeliverTx {
+func (cli *grpcClient) DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error) {
 	reqres := cli.DeliverTxAsync(tx)
 	if err := cli.Error(); err != nil {
-		return &types.ResponseDeliverTx{Code: types.CodeType_InternalError, Log: err.Error()}
+		return nil, errors.Wrap(err, types.HumanCode(types.CodeType_InternalError))
 	}
-	return reqres.Response.GetDeliverTx()
+	return reqres.Response.GetDeliverTx(), nil
 }
 
-func (cli *grpcClient) CheckTxSync(tx []byte) *types.ResponseCheckTx {
+func (cli *grpcClient) CheckTxSync(tx []byte) (*types.ResponseCheckTx, error) {
 	reqres := cli.CheckTxAsync(tx)
 	if err := cli.Error(); err != nil {
-		return &types.ResponseCheckTx{Code: types.CodeType_InternalError, Log: err.Error()}
+		return nil, errors.Wrap(err, types.HumanCode(types.CodeType_InternalError))
 	}
-	return reqres.Response.GetCheckTx()
+	return reqres.Response.GetCheckTx(), nil
 }
 
 func (cli *grpcClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery, error) {
@@ -288,12 +289,12 @@ func (cli *grpcClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery,
 	return reqres.Response.GetQuery(), cli.Error()
 }
 
-func (cli *grpcClient) CommitSync() *types.ResponseCommit {
+func (cli *grpcClient) CommitSync() (*types.ResponseCommit, error) {
 	reqres := cli.CommitAsync()
 	if err := cli.Error(); err != nil {
-		return &types.ResponseCommit{Code: types.CodeType_InternalError, Log: err.Error()}
+		return nil, errors.Wrap(err, types.HumanCode(types.CodeType_InternalError))
 	}
-	return reqres.Response.GetCommit()
+	return reqres.Response.GetCommit(), nil
 }
 
 func (cli *grpcClient) InitChainSync(params types.RequestInitChain) error {
diff --git a/client/local_client.go b/client/local_client.go
index 2a294f48..15dda8e6 100644
--- a/client/local_client.go
+++ b/client/local_client.go
@@ -166,18 +166,18 @@ func (app *localClient) SetOptionSync(key string, value string) (log string, err
 	return log, nil
 }
 
-func (app *localClient) DeliverTxSync(tx []byte) *types.ResponseDeliverTx {
+func (app *localClient) DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error) {
 	app.mtx.Lock()
 	res := app.Application.DeliverTx(tx)
 	app.mtx.Unlock()
-	return &res
+	return &res, nil
 }
 
-func (app *localClient) CheckTxSync(tx []byte) *types.ResponseCheckTx {
+func (app *localClient) CheckTxSync(tx []byte) (*types.ResponseCheckTx, error) {
 	app.mtx.Lock()
 	res := app.Application.CheckTx(tx)
 	app.mtx.Unlock()
-	return &res
+	return &res, nil
 }
 
 func (app *localClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery, error) {
@@ -187,11 +187,11 @@ func (app *localClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery,
 	return &res, nil
 }
 
-func (app *localClient) CommitSync() *types.ResponseCommit {
+func (app *localClient) CommitSync() (*types.ResponseCommit, error) {
 	app.mtx.Lock()
 	res := app.Application.Commit()
 	app.mtx.Unlock()
-	return &res
+	return &res, nil
 }
 
 func (app *localClient) InitChainSync(params types.RequestInitChain) error {
diff --git a/client/socket_client.go b/client/socket_client.go
index 64211979..7e117d22 100644
--- a/client/socket_client.go
+++ b/client/socket_client.go
@@ -3,13 +3,13 @@ package abcicli
 import (
 	"bufio"
 	"container/list"
-	"errors"
 	"fmt"
 	"net"
 	"reflect"
 	"sync"
 	"time"
 
+	"github.com/pkg/errors"
 	"github.com/tendermint/abci/types"
 	cmn "github.com/tendermint/tmlibs/common"
 )
@@ -303,22 +303,22 @@ func (cli *socketClient) SetOptionSync(key string, value string) (log string, er
 	return reqres.Response.GetSetOption().Log, nil
 }
 
-func (cli *socketClient) DeliverTxSync(tx []byte) *types.ResponseDeliverTx {
+func (cli *socketClient) DeliverTxSync(tx []byte) (*types.ResponseDeliverTx, error) {
 	reqres := cli.queueRequest(types.ToRequestDeliverTx(tx))
 	cli.FlushSync()
 	if err := cli.Error(); err != nil {
-		return &types.ResponseDeliverTx{Code: types.CodeType_InternalError, Log: err.Error()}
+		return nil, errors.Wrap(err, types.HumanCode(types.CodeType_InternalError))
 	}
-	return reqres.Response.GetDeliverTx()
+	return reqres.Response.GetDeliverTx(), nil
 }
 
-func (cli *socketClient) CheckTxSync(tx []byte) *types.ResponseCheckTx {
+func (cli *socketClient) CheckTxSync(tx []byte) (*types.ResponseCheckTx, error) {
 	reqres := cli.queueRequest(types.ToRequestCheckTx(tx))
 	cli.FlushSync()
 	if err := cli.Error(); err != nil {
-		return &types.ResponseCheckTx{Code: types.CodeType_InternalError, Log: err.Error()}
+		return nil, errors.Wrap(err, types.HumanCode(types.CodeType_InternalError))
 	}
-	return reqres.Response.GetCheckTx()
+	return reqres.Response.GetCheckTx(), nil
 }
 
 func (cli *socketClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery, error) {
@@ -327,13 +327,13 @@ func (cli *socketClient) QuerySync(req types.RequestQuery) (*types.ResponseQuery
 	return reqres.Response.GetQuery(), cli.Error()
 }
 
-func (cli *socketClient) CommitSync() *types.ResponseCommit {
+func (cli *socketClient) CommitSync() (*types.ResponseCommit, error) {
 	reqres := cli.queueRequest(types.ToRequestCommit())
 	cli.FlushSync()
 	if err := cli.Error(); err != nil {
-		return &types.ResponseCommit{Code: types.CodeType_InternalError, Log: err.Error()}
+		return nil, errors.Wrap(err, types.HumanCode(types.CodeType_InternalError))
 	}
-	return reqres.Response.GetCommit()
+	return reqres.Response.GetCommit(), nil
 }
 
 func (cli *socketClient) InitChainSync(params types.RequestInitChain) error {
diff --git a/cmd/abci-cli/abci-cli.go b/cmd/abci-cli/abci-cli.go
index cd6f05f4..e3f0daec 100644
--- a/cmd/abci-cli/abci-cli.go
+++ b/cmd/abci-cli/abci-cli.go
@@ -371,7 +371,10 @@ func cmdDeliverTx(cmd *cobra.Command, args []string) error {
 	if err != nil {
 		return err
 	}
-	res := client.DeliverTxSync(txBytes)
+	res, err := client.DeliverTxSync(txBytes)
+	if err != nil {
+		return err
+	}
 	printResponse(cmd, args, response{
 		Code: res.Code,
 		Data: res.Data,
@@ -386,7 +389,10 @@ func cmdCheckTx(cmd *cobra.Command, args []string) error {
 	if err != nil {
 		return err
 	}
-	res := client.CheckTxSync(txBytes)
+	res, err := client.CheckTxSync(txBytes)
+	if err != nil {
+		return err
+	}
 	printResponse(cmd, args, response{
 		Code: res.Code,
 		Data: res.Data,
@@ -397,7 +403,10 @@ func cmdCheckTx(cmd *cobra.Command, args []string) error {
 
 // Get application Merkle root hash
 func cmdCommit(cmd *cobra.Command, args []string) error {
-	res := client.CommitSync()
+	res, err := client.CommitSync()
+	if err != nil {
+		return err
+	}
 	printResponse(cmd, args, response{
 		Code: res.Code,
 		Data: res.Data,
diff --git a/example/dummy/dummy_test.go b/example/dummy/dummy_test.go
index efbc5af7..798da720 100644
--- a/example/dummy/dummy_test.go
+++ b/example/dummy/dummy_test.go
@@ -281,10 +281,12 @@ func runClientTests(t *testing.T, client abcicli.Client) {
 }
 
 func testClient(t *testing.T, app abcicli.Client, tx []byte, key, value string) {
-	ar := app.DeliverTxSync(tx)
+	ar, err := app.DeliverTxSync(tx)
+	require.NoError(t, err)
 	require.False(t, ar.IsErr(), ar)
 	// repeating tx doesn't raise error
-	ar = app.DeliverTxSync(tx)
+	ar, err = app.DeliverTxSync(tx)
+	require.NoError(t, err)
 	require.False(t, ar.IsErr(), ar)
 
 	// make sure query is fine
diff --git a/tests/test_app/app.go b/tests/test_app/app.go
index 67742b38..c3e9d14f 100644
--- a/tests/test_app/app.go
+++ b/tests/test_app/app.go
@@ -55,7 +55,10 @@ func setOption(client abcicli.Client, key, value string) {
 }
 
 func commit(client abcicli.Client, hashExp []byte) {
-	res := client.CommitSync()
+	res, err := client.CommitSync()
+	if err != nil {
+		panicf("client error: %v", err)
+	}
 	if res.IsErr() {
 		panicf("committing err %v\n", res)
 	}
@@ -65,7 +68,10 @@ func commit(client abcicli.Client, hashExp []byte) {
 }
 
 func deliverTx(client abcicli.Client, txBytes []byte, codeExp types.CodeType, dataExp []byte) {
-	res := client.DeliverTxSync(txBytes)
+	res, err := client.DeliverTxSync(txBytes)
+	if err != nil {
+		panicf("client error: %v", err)
+	}
 	if res.Code != codeExp {
 		panicf("DeliverTx response code was unexpected. Got %v expected %v. Log: %v", res.Code, codeExp, res.Log)
 	}
@@ -75,7 +81,10 @@ func deliverTx(client abcicli.Client, txBytes []byte, codeExp types.CodeType, da
 }
 
 /*func checkTx(client abcicli.Client, txBytes []byte, codeExp types.CodeType, dataExp []byte) {
-	res := client.CheckTxSync(txBytes)
+	res, err := client.CheckTxSync(txBytes)
+	if err != nil {
+		panicf("client error: %v", err)
+	}
 	if res.IsErr() {
 		panicf("checking tx %X: %v\nlog: %v", txBytes, res.Log)
 	}
diff --git a/types/errors.go b/types/errors.go
index 03d14578..f63d2470 100644
--- a/types/errors.go
+++ b/types/errors.go
@@ -47,3 +47,12 @@ var (
 		CodeType_BaseUnknownPubKey:        "Error (base) unknown pubkey",
 	}
 )
+
+// HumanCode transforms code into a more humane format, such as "Internal error" instead of 0.
+func HumanCode(code CodeType) string {
+	s, ok := code2string[code]
+	if !ok {
+		return "Unknown code"
+	}
+	return s
+}