diff --git a/tutorial/tutorial-10-user_defined_protocol/message.cc b/tutorial/tutorial-10-user_defined_protocol/message.cc
index c99fca22..a5dd091e 100644
--- a/tutorial/tutorial-10-user_defined_protocol/message.cc
+++ b/tutorial/tutorial-10-user_defined_protocol/message.cc
@@ -83,7 +83,7 @@ int TutorialMessage::append(const void *buf, size_t size)
 		return -1;
 	}
 
-	memcpy(this->body, buf, body_left);
+	memcpy(this->body, buf, size);
 	if (size < body_left)
 		return 0;