--- a/plugins/muc/subject.lib.lua	Fri Jun 01 08:03:12 2018 +0200
+++ b/plugins/muc/subject.lib.lua	Fri Jun 01 08:47:07 2018 +0200
@@ -101,7 +101,7 @@
 			room:save();
 			return true;
 		else
-			event.origin.send(st.error_reply(stanza, "auth", "forbidden"));
+			event.origin.send(st.error_reply(stanza, "auth", "forbidden", "You are not allowed to change the subject"));
 			return true;
 		end
 	end