diff --git a/docs/spec/ibc/mvp2.md b/docs/spec/ibc/mvp2.md
index f8ae465c3d..61590007d8 100644
--- a/docs/spec/ibc/mvp2.md
+++ b/docs/spec/ibc/mvp2.md
@@ -23,6 +23,7 @@ type Payload interface {
 }
 
 type TransferPayload struct {
+    SrcAddr  sdk.Address
     DestAddr sdk.Address
     Coins    sdk.Coins
 }
diff --git a/examples/basecoin/app/app.go b/examples/basecoin/app/app.go
index 0b5c382c6d..05a659409a 100644
--- a/examples/basecoin/app/app.go
+++ b/examples/basecoin/app/app.go
@@ -56,7 +56,7 @@ func NewBasecoinApp(logger log.Logger, db dbm.DB) *BasecoinApp {
 	// add handlers
 	coinKeeper := bank.NewCoinKeeper(app.accountMapper)
 	coolMapper := cool.NewMapper(app.capKeyMainStore)
-	ibcMapper := ibc.NewIBCMapper(app.capKeyIBCStore)
+	ibcMapper := ibc.NewIBCMapper(app.cdc, app.capKeyIBCStore)
 	app.Router().
 		AddRoute("bank", bank.NewHandler(coinKeeper)).
 		AddRoute("cool", cool.NewHandler(coinKeeper, coolMapper)).
diff --git a/x/ibc/ibc_test.go b/x/ibc/ibc_test.go
index 478c5e5a9f..bec08fb564 100644
--- a/x/ibc/ibc_test.go
+++ b/x/ibc/ibc_test.go
@@ -74,7 +74,7 @@ func makeCodec() *wire.Codec {
 }
 
 func TestIBC(t *testing.T) {
-	var _ = makeCodec()
+	cdc := makeCodec()
 
 	key := sdk.NewKVStoreKey("ibc")
 	ctx := defaultContext(key)
@@ -92,7 +92,7 @@ func TestIBC(t *testing.T) {
 	assert.Nil(t, err)
 	assert.Equal(t, mycoins, coins)
 
-	ibcm := NewIBCMapper(key)
+	ibcm := NewIBCMapper(cdc, key)
 	h := NewHandler(ibcm, ck)
 	packet := IBCPacket{
 		SrcAddr:   src,
diff --git a/x/ibc/mapper.go b/x/ibc/mapper.go
index 49714ec162..1e8f9de253 100644
--- a/x/ibc/mapper.go
+++ b/x/ibc/mapper.go
@@ -14,10 +14,8 @@ type IBCMapper struct {
 
 // XXX: The IBCMapper should not take a CoinKeeper. Rather have the CoinKeeper
 // take an IBCMapper.
-func NewIBCMapper(key sdk.StoreKey) IBCMapper {
+func NewIBCMapper(cdc *wire.Codec, key sdk.StoreKey) IBCMapper {
 	// XXX: How are these codecs supposed to work?
-	cdc := wire.NewCodec()
-
 	return IBCMapper{
 		key: key,
 		cdc: cdc,
@@ -59,25 +57,34 @@ func (ibcm IBCMapper) ReceiveIBCPacket(ctx sdk.Context, packet IBCPacket) sdk.Er
 // --------------------------
 // Functions for accessing the underlying KVStore.
 
+func marshalBinaryPanic(cdc *wire.Codec, value interface{}) []byte {
+	res, err := cdc.MarshalBinary(value)
+	if err != nil {
+		panic(err)
+	}
+	return res
+}
+
+func unmarshalBinaryPanic(cdc *wire.Codec, bz []byte, ptr interface{}) {
+	err := cdc.UnmarshalBinary(bz, ptr)
+	if err != nil {
+		panic(err)
+	}
+}
+
 func (ibcm IBCMapper) GetIngressSequence(ctx sdk.Context, srcChain string) int64 {
 	store := ctx.KVStore(ibcm.key)
 	key := IngressSequenceKey(srcChain)
 
 	bz := store.Get(key)
 	if bz == nil {
-		zero, err := ibcm.cdc.MarshalBinary(int64(0))
-		if err != nil {
-			panic(err)
-		}
+		zero := marshalBinaryPanic(ibcm.cdc, int64(0))
 		store.Set(key, zero)
 		return 0
 	}
 
 	var res int64
-	err := ibcm.cdc.UnmarshalBinary(bz, &res)
-	if err != nil {
-		panic(err)
-	}
+	unmarshalBinaryPanic(ibcm.cdc, bz, &res)
 	return res
 }
 
@@ -85,10 +92,7 @@ func (ibcm IBCMapper) SetIngressSequence(ctx sdk.Context, srcChain string, seque
 	store := ctx.KVStore(ibcm.key)
 	key := IngressSequenceKey(srcChain)
 
-	bz, err := ibcm.cdc.MarshalBinary(sequence)
-	if err != nil {
-		panic(err)
-	}
+	bz := marshalBinaryPanic(ibcm.cdc, sequence)
 	store.Set(key, bz)
 }
 
@@ -96,17 +100,12 @@ func (ibcm IBCMapper) SetIngressSequence(ctx sdk.Context, srcChain string, seque
 func (ibcm IBCMapper) getEgressLength(store sdk.KVStore, destChain string) int64 {
 	bz := store.Get(EgressLengthKey(destChain))
 	if bz == nil {
-		zero, err := ibcm.cdc.MarshalBinary(int64(0))
-		if err != nil {
-			panic(err)
-		}
+		zero := marshalBinaryPanic(ibcm.cdc, int64(0))
 		store.Set(EgressLengthKey(destChain), zero)
 		return 0
 	}
 	var res int64
-	if err := ibcm.cdc.UnmarshalBinary(bz, &res); err != nil {
-		panic(err)
-	}
+	unmarshalBinaryPanic(ibcm.cdc, bz, &res)
 	return res
 }
 
diff --git a/x/ibc/types.go b/x/ibc/types.go
index 5af22220a2..495d2a9009 100644
--- a/x/ibc/types.go
+++ b/x/ibc/types.go
@@ -35,6 +35,9 @@ func (ibcp IBCPacket) ValidateBasic() sdk.Error {
 	if ibcp.SrcChain == ibcp.DestChain {
 		return ErrIdenticalChains().Trace("")
 	}
+	if !ibcp.Coins.IsValid() {
+		return sdk.ErrInvalidCoins("")
+	}
 	return nil
 }
 
@@ -56,7 +59,7 @@ func (msg IBCTransferMsg) Get(key interface{}) interface{} {
 
 func (msg IBCTransferMsg) GetSignBytes() []byte {
 	cdc := wire.NewCodec()
-	bz, err := cdc.MarshalBinary(msg.IBCPacket)
+	bz, err := cdc.MarshalBinary(msg)
 	if err != nil {
 		panic(err)
 	}
@@ -93,7 +96,7 @@ func (msg IBCReceiveMsg) Get(key interface{}) interface{} {
 
 func (msg IBCReceiveMsg) GetSignBytes() []byte {
 	cdc := wire.NewCodec()
-	bz, err := cdc.MarshalBinary(msg.IBCPacket)
+	bz, err := cdc.MarshalBinary(msg)
 	if err != nil {
 		panic(err)
 	}