diff --git a/core/modules/forum/tests/Drupal/forum/Tests/ForumManagerTest.php b/core/modules/forum/tests/Drupal/forum/Tests/ForumManagerTest.php
index c5d2d11..3389e6d 100644
--- a/core/modules/forum/tests/Drupal/forum/Tests/ForumManagerTest.php
+++ b/core/modules/forum/tests/Drupal/forum/Tests/ForumManagerTest.php
@@ -10,6 +10,7 @@
 use Drupal\Tests\UnitTestCase;
 
 // @todo Remove once the constants are replaced with constants on classes.
+//   https://drupal.org/node/2169361
 if (!defined('COMMENT_OPEN')) {
   define('COMMENT_OPEN', 2);
 }