diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index 820053b446a..39ba13bfb25 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -1679,13 +1679,16 @@ function forum_subscribed_users($course, $forum, $groupid=0, $cache=false) {
                                AND u.deleted <> 1  $groupselect
                           ORDER BY u.email ASC");
     }
+	// Guest user should never be subscribed to a forum.
+	if ($guest = guest_user()) {
+		unset($results[$guest->id]);
+	}
 
     if ($cache) {
         $resultscache[$forum->id][$groupid] = $results;
     }
 
     return $results;
-    
 }