diff --git a/mod/forum/rsslib.php b/mod/forum/rsslib.php
index 9f9057b713e..7b051a65bb0 100644
--- a/mod/forum/rsslib.php
+++ b/mod/forum/rsslib.php
@@ -43,7 +43,7 @@ function forum_rss_get_feed($context, $args) {
         return null;
     }
 
-    $forumid = $args[3];
+    $forumid  = clean_param($args[3], PARAM_INT);
 
     $uservalidated = false;