diff --git a/phpBB/viewtopic.php b/phpBB/viewtopic.php
index 4c6520b6f5..920ec48611 100644
--- a/phpBB/viewtopic.php
+++ b/phpBB/viewtopic.php
@@ -338,7 +338,7 @@ $user->setup('viewtopic', $topic_data['forum_style']);
 
 $overrides_f_read = false;
 $overrides_forum_password = false;
-$topic_tracking_info = isset($topic_tracking_info) ? $topic_tracking_info : NULL;
+$topic_tracking_info = isset($topic_tracking_info) ? $topic_tracking_info : null;
 /**
 * Event to apply extra permissions and to override original phpBB's f_read permission and forum password check
 * on viewtopic access