diff --git a/plugins/ibc/ibc.go b/plugins/ibc/ibc.go
index 0c203eb97d..7662e9ec91 100644
--- a/plugins/ibc/ibc.go
+++ b/plugins/ibc/ibc.go
@@ -66,7 +66,8 @@ const (
 	IBCCodeChainAlreadyExists  = abci.CodeType(1002)
 	IBCCodePacketAlreadyExists = abci.CodeType(1003)
 	IBCCodeUnknownHeight       = abci.CodeType(1004)
-	IBCCodeInvalidProof        = abci.CodeType(1005)
+	IBCCodeInvalidCommit       = abci.CodeType(1005)
+	IBCCodeInvalidProof        = abci.CodeType(1006)
 )
 
 var _ = wire.RegisterInterface(
@@ -154,7 +155,7 @@ func (ibc *IBCPlugin) RunTx(store types.KVStore, ctx types.CallContext, txBytes
 	var tx IBCTx
 	err := wire.ReadBinaryBytes(txBytes, &tx)
 	if err != nil {
-		return abci.ErrBaseEncodingError.AppendLog("Error decoding tx: " + err.Error()).PrependLog("IBCTx Error: ")
+		return abci.ErrBaseEncodingError.AppendLog("Error decoding tx: " + err.Error())
 	}
 
 	// Validate tx
@@ -265,7 +266,8 @@ func (sm *IBCStateMachine) runUpdateChainTx(tx IBCUpdateChainTx) {
 	// Check commit against last known state & validators
 	err = verifyCommit(chainState, &tx.Header, &tx.Commit)
 	if err != nil {
-		sm.res = abci.ErrInternalError.AppendLog(cmn.Fmt("Invalid Commit: %v", err.Error()))
+		sm.res.Code = IBCCodeInvalidCommit
+		sm.res.Log = cmn.Fmt("Invalid Commit: %v", err.Error())
 		return
 	}
 
diff --git a/plugins/ibc/ibc_test.go b/plugins/ibc/ibc_test.go
index 3074c93443..0b1a71fb01 100644
--- a/plugins/ibc/ibc_test.go
+++ b/plugins/ibc/ibc_test.go
@@ -11,6 +11,7 @@ import (
 	"github.com/tendermint/basecoin/testutils"
 	"github.com/tendermint/basecoin/types"
 	cmn "github.com/tendermint/go-common"
+	crypto "github.com/tendermint/go-crypto"
 	"github.com/tendermint/go-wire"
 	eyes "github.com/tendermint/merkleeyes/client"
 	tm "github.com/tendermint/tendermint/types"
@@ -87,7 +88,7 @@ func TestIBCPlugin(t *testing.T) {
 			Genesis: "<THIS IS NOT JSON>",
 		},
 	}}))
-	assert.Equal(t, res.Code, IBCCodeEncodingError)
+	assert.Equal(t, IBCCodeEncodingError, res.Code)
 	t.Log(">>", strings.Join(store.GetLogLines(), "\n"))
 	store.ClearLogLines()
 
@@ -109,7 +110,7 @@ func TestIBCPlugin(t *testing.T) {
 			Genesis: string(genDocJSON_1),
 		},
 	}}))
-	assert.Equal(t, res.Code, IBCCodeChainAlreadyExists, res.Log)
+	assert.Equal(t, IBCCodeChainAlreadyExists, res.Code, res.Log)
 	t.Log(">>", strings.Join(store.GetLogLines(), "\n"))
 	store.ClearLogLines()
 
@@ -123,7 +124,7 @@ func TestIBCPlugin(t *testing.T) {
 			Payload:    []byte("hello world"),
 		},
 	}}))
-	assert.Equal(t, res.Code, abci.CodeType(0), res.Log)
+	assert.Equal(t, abci.CodeType_OK, res.Code, res.Log)
 	t.Log(">>", strings.Join(store.GetLogLines(), "\n"))
 	store.ClearLogLines()
 
@@ -137,7 +138,7 @@ func TestIBCPlugin(t *testing.T) {
 			Payload:    []byte("hello world"),
 		},
 	}}))
-	assert.Equal(t, res.Code, IBCCodePacketAlreadyExists, res.Log)
+	assert.Equal(t, IBCCodePacketAlreadyExists, res.Code, res.Log)
 	t.Log(">>", strings.Join(store.GetLogLines(), "\n"))
 	store.ClearLogLines()
 
@@ -179,7 +180,20 @@ func TestIBCPlugin(t *testing.T) {
 		Header: header,
 		Commit: commit,
 	}}))
-	assert.Equal(t, res.Code, abci.CodeType(0), res.Log)
+	assert.Equal(t, abci.CodeType_OK, res.Code, res.Log)
+	t.Log(">>", strings.Join(store.GetLogLines(), "\n"))
+	store.ClearLogLines()
+
+	// Update a chain with a broken commit
+	// Modify the first byte of the first signature
+	sig := commit.Precommits[0].Signature.(crypto.SignatureEd25519)
+	sig[0] += 1
+	commit.Precommits[0].Signature = sig
+	res = ibcPlugin.RunTx(store, ctx, wire.BinaryBytes(struct{ IBCTx }{IBCUpdateChainTx{
+		Header: header,
+		Commit: commit,
+	}}))
+	assert.Equal(t, IBCCodeInvalidCommit, res.Code, res.Log)
 	t.Log(">>", strings.Join(store.GetLogLines(), "\n"))
 	store.ClearLogLines()
 }