diff --git a/phpBB/viewtopic.php b/phpBB/viewtopic.php
index a0982ff07e..add38f5f1b 100644
--- a/phpBB/viewtopic.php
+++ b/phpBB/viewtopic.php
@@ -23,10 +23,14 @@
 include('extension.inc');
 include('common.'.$phpEx);
 
-if(!isset($topic_id))
+if(!isset($HTTP_GET_VARS['topic']))  // For backward compatibility
 {
 	$topic_id = $HTTP_GET_VARS[POST_TOPIC_URL];
 }
+else
+{
+	$topic_id = $HTTP_GET_VARS['topic'];
+}
 
 $is_moderator = 0;