diff --git a/classes/readtracking.php b/classes/readtracking.php
index 3b368c3dff..fbd1292538 100644
--- a/classes/readtracking.php
+++ b/classes/readtracking.php
@@ -130,7 +130,7 @@ public static function moodleoverflow_mark_moodleoverflow_read($cm, $userid = nu
         $discussions = moodleoverflow_get_discussions_unread($cm);
 
         // Iterate through all of this discussions.
-        foreach ($discussions as $discussionid) {
+        foreach ($discussions as $discussionid => $unread) {
             // Mark the discussion as read.
             $markedcheck = self::moodleoverflow_mark_discussion_read($discussionid, context_module::instance($cm->id), $userid);
             moodleoverflow_throw_exception_with_check($markedcheck !== true, 'markreadfailed');