Index: upstream/phpbb/current/includes/functions.php
===================================================================
--- upstream/phpbb/current/includes/functions.php	(revision 246)
+++ upstream/phpbb/current/includes/functions.php	(working copy)
@@ -3609,6 +3609,11 @@
 				$user->setup();
 			}
 
+			if ($msg_text == 'NO_FORUM' || $msg_text == 'NO_TOPIC' || $msg_text == 'NO_USER')
+			{
+				header("HTTP/1.x 404 Not Found");
+			}
+
 			$msg_text = (!empty($user->lang[$msg_text])) ? $user->lang[$msg_text] : $msg_text;
 			$msg_title = (!isset($msg_title)) ? $user->lang['INFORMATION'] : ((!empty($user->lang[$msg_title])) ? $user->lang[$msg_title] : $msg_title);