diff --git a/proto/proto.go b/proto/proto.go
index d912616..2699399 100644
--- a/proto/proto.go
+++ b/proto/proto.go
@@ -38,14 +38,14 @@ func (c *protoCodec) Marshal(v interface{}, opts ...codec.Option) ([]byte, error
 		return m.Data, nil
 	}
 
-	switch v.(type) {
-	case proto.Message, newproto.Message:
-		break
-	default:
-		return nil, codec.ErrInvalidMessage
+	switch m := v.(type) {
+	case proto.Message:
+		return proto.Marshal(m)
+	case newproto.Message:
+		return proto.Marshal(m)
 	}
 
-	return proto.Marshal(v.(proto.Message))
+	return nil, codec.ErrInvalidMessage
 }
 
 func (c *protoCodec) Unmarshal(d []byte, v interface{}, opts ...codec.Option) error {
@@ -67,14 +67,15 @@ func (c *protoCodec) Unmarshal(d []byte, v interface{}, opts ...codec.Option) er
 		return nil
 	}
 
-	switch v.(type) {
-	case proto.Message, newproto.Message:
-		break
-	default:
-		return codec.ErrInvalidMessage
+	switch m := v.(type) {
+	case proto.Message:
+		return proto.Unmarshal(d, m)
+	case newproto.Message:
+		return proto.Unmarshal(d, m)
+
 	}
 
-	return proto.Unmarshal(d, v.(proto.Message))
+	return codec.ErrInvalidMessage
 }
 
 func (c *protoCodec) ReadHeader(conn io.Reader, m *codec.Message, t codec.MessageType) error {