diff --git a/mod/forum/classes/subscriptions.php b/mod/forum/classes/subscriptions.php
index ca4c7df2f90..af3f57e1e6f 100644
--- a/mod/forum/classes/subscriptions.php
+++ b/mod/forum/classes/subscriptions.php
@@ -850,7 +850,7 @@ class subscriptions {
             // User does not have permission to unsubscribe from this discussion at all.
             $discussionsubscribe = true;
         } else {
-            if (isset($discussion) && \mod_forum\subscriptions::is_subscribed($USER->id, $forum, $discussionid, $cm)) {
+            if (isset($discussionid) && self::is_subscribed($USER->id, $forum, $discussionid, $cm)) {
                 // User is subscribed to the discussion - continue the subscription.
                 $discussionsubscribe = true;
             } else if (!isset($discussionid) && \mod_forum\subscriptions::is_subscribed($USER->id, $forum, null, $cm)) {