diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 812172a567b..4b7a8ccdf52 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -383,7 +383,7 @@ WHERE
  * @return string A unique message-id
  */
 function forum_get_email_message_id($postid, $usertoid, $hostname) {
-    return '<'.hash('sha256',$postid.'to'.$usertoid.'@'.$hostname).'>';
+    return '<'.hash('sha256',$postid.'to'.$usertoid).'@'.$hostname.'>';
 }
 
 /**