diff --git a/dispatcher.go b/dispatcher.go
index 4eee2fc..f563f51 100644
--- a/dispatcher.go
+++ b/dispatcher.go
@@ -22,6 +22,7 @@ import (
 //
 // See examples for details.
 type Dispatcher struct {
+	mu         sync.RWMutex
 	serviceMap map[string]*serviceData
 }
 
@@ -60,6 +61,8 @@ func NewDispatcher() *Dispatcher {
 //
 // See examples for details.
 func (d *Dispatcher) AddFunc(funcName string, f interface{}) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
 	sd, ok := d.serviceMap[""]
 	if !ok {
 		sd = &serviceData{
@@ -90,6 +93,8 @@ func (d *Dispatcher) AddFunc(funcName string, f interface{}) {
 //
 // All public methods must conform requirements described in AddFunc().
 func (d *Dispatcher) AddService(serviceName string, service interface{}) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
 	if serviceName == "" {
 		logPanic("gorpc.Dispatcher: serviceName cannot be empty")
 	}
@@ -242,7 +247,7 @@ func validateType(t reflect.Type) (err error) {
 	})
 
 	switch t.Kind() {
-	case reflect.Chan, reflect.Func, reflect.Interface, reflect.UnsafePointer:
+	case reflect.Chan, reflect.Func, reflect.UnsafePointer:
 		err = fmt.Errorf("%s. Found [%s]", t.Kind(), t)
 		return err
 	case reflect.Array, reflect.Slice:
@@ -308,18 +313,14 @@ func init() {
 // The returned HandlerFunc must be assigned to Server.Handler or
 // passed to New*Server().
 func (d *Dispatcher) NewHandlerFunc() HandlerFunc {
-	if len(d.serviceMap) == 0 {
-		logPanic("gorpc.Dispatcher: register at least one service before calling HandlerFunc()")
-	}
-
-	serviceMap := copyServiceMap(d.serviceMap)
-
 	return func(clientAddr string, request interface{}) interface{} {
 		req, ok := request.(*dispatcherRequest)
 		if !ok {
 			logPanic("gorpc.Dispatcher: unsupported request type received from the client: %T", request)
 		}
-		return dispatchRequest(serviceMap, clientAddr, req)
+		d.mu.RLock()
+		defer d.mu.RUnlock()
+		return dispatchRequest(d.serviceMap, clientAddr, req)
 	}
 }
 
@@ -446,13 +447,9 @@ type DispatcherClient struct {
 	serviceName string
 }
 
-// NewFuncClient returns a client suitable for calling functions registered
-// via AddFunc().
-func (d *Dispatcher) NewFuncClient(c *Client) *DispatcherClient {
-	if len(d.serviceMap) == 0 || d.serviceMap[""] == nil {
-		logPanic("gorpc.Dispatcher: register at least one function with AddFunc() before calling NewFuncClient()")
-	}
-
+// NewDispatcherFuncClient returns a client suitable for calling functions
+// registered via AddFunc().
+func NewDispatcherFuncClient(c *Client) *DispatcherClient {
 	return &DispatcherClient{
 		c: c,
 	}
@@ -462,15 +459,35 @@ func (d *Dispatcher) NewFuncClient(c *Client) *DispatcherClient {
 // of the service with name serviceName registered via AddService().
 //
 // It is safe creating multiple service clients over a single underlying client.
+func NewDispatcherServiceClient(serviceName string, c *Client) *DispatcherClient {
+	return &DispatcherClient{
+		c:           c,
+		serviceName: serviceName,
+	}
+}
+
+// NewFuncClient checks and returns a client suitable for calling functions
+// registered via AddFunc().
+func (d *Dispatcher) NewFuncClient(c *Client) *DispatcherClient {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
+	if len(d.serviceMap) == 0 || d.serviceMap[""] == nil {
+		logPanic("gorpc.Dispatcher: register at least one function with AddFunc() before calling NewFuncClient()")
+	}
+
+	return NewDispatcherFuncClient(c)
+}
+
+// NewServiceClient checks and returns a client suitable for calling methods
+// of the service with name serviceName registered via AddService().
 func (d *Dispatcher) NewServiceClient(serviceName string, c *Client) *DispatcherClient {
+	d.mu.RLock()
+	defer d.mu.RUnlock()
 	if len(d.serviceMap) == 0 || d.serviceMap[serviceName] == nil {
 		logPanic("gorpc.Dispatcher: service [%s] must be registered with AddService() before calling NewServiceClient()", serviceName)
 	}
 
-	return &DispatcherClient{
-		c:           c,
-		serviceName: serviceName,
-	}
+	return NewDispatcherServiceClient(serviceName, c)
 }
 
 // Call calls the given function with the given request.
diff --git a/dispatcher_test.go b/dispatcher_test.go
index 1d59f05..b740246 100644
--- a/dispatcher_test.go
+++ b/dispatcher_test.go
@@ -3,7 +3,6 @@ package gorpc
 import (
 	"bytes"
 	"fmt"
-	"io"
 	"reflect"
 	"sync/atomic"
 	"testing"
@@ -11,13 +10,6 @@ import (
 	"unsafe"
 )
 
-func TestDispatcherNewHandlerNoFuncs(t *testing.T) {
-	d := NewDispatcher()
-	testPanic(t, func() {
-		d.NewHandlerFunc()
-	})
-}
-
 func TestDispatcherNewFuncClientNoFuncs(t *testing.T) {
 	c := NewTCPClient(getRandomAddr())
 
@@ -92,16 +84,6 @@ func TestDispatcherChanArg(t *testing.T) {
 	})
 }
 
-func TestDispatcherInterfaceArg(t *testing.T) {
-	d := NewDispatcher()
-	testPanic(t, func() {
-		d.AddFunc("foo", func(req io.Reader) {})
-	})
-	testPanic(t, func() {
-		d.AddFunc("foo", func(req interface{}) {})
-	})
-}
-
 func TestDispatcherUnsafePointerArg(t *testing.T) {
 	d := NewDispatcher()
 	testPanic(t, func() {
@@ -123,16 +105,6 @@ func TestDispatcherChanRes(t *testing.T) {
 	})
 }
 
-func TestDispatcherInterfaceRes(t *testing.T) {
-	d := NewDispatcher()
-	testPanic(t, func() {
-		d.AddFunc("foo", func() (res io.Reader) { return })
-	})
-	testPanic(t, func() {
-		d.AddFunc("foo", func() (res interface{}) { return })
-	})
-}
-
 func TestDispatcherUnsafePointerRes(t *testing.T) {
 	d := NewDispatcher()
 	testPanic(t, func() {
@@ -143,7 +115,7 @@ func TestDispatcherUnsafePointerRes(t *testing.T) {
 func TestDispatcherStructWithInvalidFields(t *testing.T) {
 	type InvalidMsg struct {
 		B int
-		A io.Reader
+		A chan bool
 	}
 
 	d := NewDispatcher()
@@ -152,13 +124,6 @@ func TestDispatcherStructWithInvalidFields(t *testing.T) {
 	})
 }
 
-func TestDispatcherInvalidMap(t *testing.T) {
-	d := NewDispatcher()
-	testPanic(t, func() {
-		d.AddFunc("foo", func(req map[string]interface{}) {})
-	})
-}
-
 func TestDispatcherPassStructArgByValue(t *testing.T) {
 	type RequestType struct {
 		a int
@@ -289,6 +254,26 @@ func TestDispatcherInvalidArgType(t *testing.T) {
 	})
 }
 
+func TestDispatcherFuncLater(t *testing.T) {
+	d := NewDispatcher()
+	d.AddFunc("foo", func(request string) {})
+	testDispatcherFunc(t, d, func(dc *DispatcherClient) {
+		res, err := dc.Call("foo", nil)
+		if err == nil {
+			t.Fatalf("Expected non-nil error")
+		}
+		if res != nil {
+			t.Fatalf("Expected nil response. Got %+v", res)
+		}
+
+		d.AddFunc("foo0", func() {})
+		_, err = dc.Call("foo0", nil)
+		if err != nil {
+			t.Fatalf("Expected nil error")
+		}
+	})
+}
+
 func TestDispatcherUnknownFuncCall(t *testing.T) {
 	d := NewDispatcher()
 	d.AddFunc("foo", func(request string) {})
@@ -987,6 +972,29 @@ func TestDispatcherServiceUnknownMethodCall(t *testing.T) {
 	testDispatcherService(t, d, "qwerty", func(dc *DispatcherClient) { testUnknownFuncs(t, dc) })
 }
 
+func TestDispatcherServiceLater(t *testing.T) {
+	d := NewDispatcher()
+	c, s := getClientServer(t, d)
+	defer s.Stop()
+	defer c.Stop()
+
+	dc := NewDispatcherServiceClient("qwerty", c)
+
+	res, err := dc.Call("Get", nil)
+	if err == nil {
+		t.Fatalf("Error expected")
+	}
+	if res != nil {
+		t.Fatalf("Expected nil response. Got %+v", res)
+	}
+
+	d.AddService("qwerty", &testService{})
+	_, err = dc.Call("Get", nil)
+	if err != nil {
+		t.Fatalf("Expected nil error")
+	}
+}
+
 func TestDispatcherServicePrivateMethodCall(t *testing.T) {
 	service := &testService{}