diff --git a/mod/forum/lib.php b/mod/forum/lib.php
index e3547a4af9a..e9248502478 100644
--- a/mod/forum/lib.php
+++ b/mod/forum/lib.php
@@ -5071,7 +5071,7 @@ function forum_user_can_see_post($forum, $discussion, $post, $user=NULL, $cm=NUL
         $user = $USER;
     }
 
-    $canviewdiscussion = !empty($cm->cache->caps['mod/forum:viewdiscussion']) || has_capability('mod/forum:viewdiscussion', $modcontext, $user->id);
+    $canviewdiscussion = !empty($cm->cache->caps['mod/forum:viewdiscussion']) || has_capability('mod/forum:viewdiscussion', get_context_instance(CONTEXT_MODULE, $cm->id), $user->id);
     if (!$canviewdiscussion && !has_all_capabilities(array('moodle/user:viewdetails', 'moodle/user:readuserposts'), get_context_instance(CONTEXT_USER, $post->userid))) {
         return false;
     }