diff --git a/mock.go b/mock.go
index 70c4f98..6a5d334 100644
--- a/mock.go
+++ b/mock.go
@@ -61,6 +61,7 @@ type ExpectedRequest struct {
 	delay time.Duration
 	rsp   interface{}
 	req   client.Request
+	rspct string
 }
 
 // WillDelayFor allows to specify duration for which it will delay result. May
@@ -77,8 +78,9 @@ func (e *ExpectedRequest) WillReturnError(err error) *ExpectedRequest {
 }
 
 // WillReturnResponse allows to set a response for expected client.Call
-func (e *ExpectedRequest) WillReturnResponse(rsp interface{}) *ExpectedRequest {
+func (e *ExpectedRequest) WillReturnResponse(ct string, rsp interface{}) *ExpectedRequest {
 	e.rsp = rsp
+	e.rspct = ct
 	return e
 }
 
@@ -133,11 +135,6 @@ func (c *MockClient) Call(ctx context.Context, req client.Request, rsp interface
 		ct = options.ContentType
 	}
 
-	cf, err := c.newCodec(ct)
-	if err != nil {
-		return errors.BadRequest("go.micro.client", err.Error())
-	}
-
 	for _, e := range c.expected {
 		er, ok := e.(*ExpectedRequest)
 		if !ok {
@@ -166,6 +163,10 @@ func (c *MockClient) Call(ctx context.Context, req client.Request, rsp interface
 		src := er.req.Body()
 		switch reqbody := er.req.Body().(type) {
 		case []byte:
+			cf, err := c.newCodec(ct)
+			if err != nil {
+				return errors.BadRequest("go.micro.client", err.Error())
+			}
 			src, err = rutil.Zero(req.Body())
 			if err == nil {
 				err = cf.Unmarshal(reqbody, src)
@@ -173,10 +174,6 @@ func (c *MockClient) Call(ctx context.Context, req client.Request, rsp interface
 			if err != nil {
 				return errors.BadRequest("go.micro.client", err.Error())
 			}
-		case client.Request:
-			break
-		default:
-			return errors.BadRequest("go.micro.client", "unknown request passed: %v", reqbody)
 		}
 
 		if !reflect.DeepEqual(req.Body(), src) {
@@ -189,6 +186,13 @@ func (c *MockClient) Call(ctx context.Context, req client.Request, rsp interface
 
 		switch rspbody := er.rsp.(type) {
 		case []byte:
+			if er.rspct != "" {
+				ct = er.rspct
+			}
+			cf, err := c.newCodec(ct)
+			if err != nil {
+				return errors.BadRequest("go.micro.client", err.Error())
+			}
 			if err = cf.Unmarshal(rspbody, rsp); err != nil {
 				return errors.BadRequest("go.micro.client", err.Error())
 			}