diff --git a/rpc-pool.go b/rpc-pool.go
index bd7bc46..bac577e 100644
--- a/rpc-pool.go
+++ b/rpc-pool.go
@@ -61,7 +61,7 @@ func (g *RemoteGrain) GetId() CartId {
 }
 
 func (g *RemoteGrain) GetCurrentState() ([]byte, error) {
-	return g.Call(RemoteGetState, g.Id, RemoteGetStateReply, nil)
+	return g.Call(RemoteGetState, g.Id, RemoteGetStateReply, []byte{})
 }
 
 func NewRemoteGrainPool(addr string) *RemoteGrainPool {
diff --git a/synced-pool.go b/synced-pool.go
index b87dc92..aa3b233 100644
--- a/synced-pool.go
+++ b/synced-pool.go
@@ -263,7 +263,7 @@ func (h *RemoteHost) Negotiate(knownHosts []string) ([]string, error) {
 }
 
 func (g *RemoteHost) GetCartMappings() ([]CartId, error) {
-	data, err := g.Call(GetCartIds, CartIdsResponse, nil)
+	data, err := g.Call(GetCartIds, CartIdsResponse, []byte{})
 	if err != nil {
 		return nil, err
 	}
@@ -359,7 +359,7 @@ func (p *SyncedPool) addRemoteHost(address string, remote *RemoteHost) error {
 }
 
 func (h *RemoteHost) Ping() error {
-	_, err := h.Call(Ping, Pong, nil)
+	_, err := h.Call(Ping, Pong, []byte{})
 
 	if err != nil {
 		h.MissedPings++
@@ -379,7 +379,7 @@ func (p *SyncedPool) AddRemote(host string) error {
 	if err != nil {
 		log.Printf("Error connecting to remote %s: %v\n", host, err)
 	}
-	_, err = client.Call(Ping, Pong, nil)
+	_, err = client.Call(Ping, Pong, []byte{})
 
 	if err != nil {
 		log.Printf("Error pinging remote %s: %v\n", host, err)
diff --git a/tcp-cart-client.go b/tcp-cart-client.go
index 246d2cd..cb46f5a 100644
--- a/tcp-cart-client.go
+++ b/tcp-cart-client.go
@@ -31,7 +31,7 @@ type CartTCPClient struct {
 	Errors     chan error
 	ErrorCount int
 	address    string
-	*PacketQueue
+	*CartPacketQueue
 }
 
 func NewCartTCPClient(address string) (*CartTCPClient, error) {
@@ -40,11 +40,11 @@ func NewCartTCPClient(address string) (*CartTCPClient, error) {
 		return nil, err
 	}
 	return &CartTCPClient{
-		Errors:      make(chan error),
-		ErrorCount:  0,
-		Conn:        connection,
-		address:     address,
-		PacketQueue: NewPacketQueue(connection),
+		Errors:          make(chan error),
+		ErrorCount:      0,
+		Conn:            connection,
+		address:         address,
+		CartPacketQueue: NewCartPacketQueue(connection),
 	}, nil
 }
 
@@ -95,7 +95,7 @@ func (m *CartTCPClient) Call(messageType uint32, id CartId, responseType uint32,
 	if err != nil {
 		return nil, err
 	}
-	packet, err := m.Expect(responseType, time.Second)
+	packet, err := m.Expect(responseType, id, time.Second)
 	if err != nil {
 		return nil, err
 	}
diff --git a/tcp-cart_test.go b/tcp-cart_test.go
new file mode 100644
index 0000000..04cc763
--- /dev/null
+++ b/tcp-cart_test.go
@@ -0,0 +1,47 @@
+package main
+
+import (
+	"log"
+	"testing"
+)
+
+func TestCartTcpHelpers(t *testing.T) {
+
+	server, err := CartListen("localhost:51337")
+	if err != nil {
+		t.Errorf("Error listening: %v\n", err)
+	}
+	client, err := CartDial("localhost:51337")
+	if err != nil {
+		t.Errorf("Error dialing: %v\n", err)
+	}
+	var messageData string
+	server.ListenFor(1, func(id CartId, data []byte) error {
+		log.Printf("Received message: %s\n", string(data))
+		messageData = string(data)
+		return nil
+	})
+	server.HandleCall(2, func(id CartId, data []byte) (uint32, []byte, error) {
+		log.Printf("Received call: %s\n", string(data))
+		return 3, []byte("Hello, client!"), nil
+	})
+	server.HandleCall(Ping, func(id CartId, data []byte) (uint32, []byte, error) {
+		return Pong, nil, nil
+	})
+	id := ToCartId("kalle")
+	client.SendPacket(1, id, []byte("Hello, world!"))
+	answer, err := client.Call(2, id, 3, []byte("Hello, server!"))
+	if err != nil {
+		t.Errorf("Error calling: %v\n", err)
+	}
+	_, err = client.Call(Ping, id, Pong, nil)
+	if err != nil {
+		t.Errorf("Error calling: %v\n", err)
+	}
+	if string(answer) != "Hello, client!" {
+		t.Errorf("Expected answer 'Hello, client!', got %s\n", string(answer))
+	}
+	if messageData != "Hello, world!" {
+		t.Errorf("Expected message 'Hello, world!', got %s\n", messageData)
+	}
+}
diff --git a/tcp-mux_test.go b/tcp-mux_test.go
index 98da91f..bc9c908 100644
--- a/tcp-mux_test.go
+++ b/tcp-mux_test.go
@@ -25,12 +25,19 @@ func TestTcpHelpers(t *testing.T) {
 		log.Printf("Received call: %s\n", string(data))
 		return 3, []byte("Hello, client!"), nil
 	})
+	server.HandleCall(Ping, func(data []byte) (uint32, []byte, error) {
+		return Pong, nil, nil
+	})
 
 	client.SendPacket(1, []byte("Hello, world!"))
 	answer, err := client.Call(2, 3, []byte("Hello, server!"))
 	if err != nil {
 		t.Errorf("Error calling: %v\n", err)
 	}
+	_, err = client.Call(Ping, Pong, nil)
+	if err != nil {
+		t.Errorf("Error calling: %v\n", err)
+	}
 	if string(answer) != "Hello, client!" {
 		t.Errorf("Expected answer 'Hello, client!', got %s\n", string(answer))
 	}