diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index b2b891be66..2d94bd14a7 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -4270,7 +4270,7 @@ function obtain_users_online_string($online_users, $item_id = 0, $item = 'forum'
 				USERS_TABLE	=> 'u',
 			),
 			'WHERE'		=> $db->sql_in_set('u.user_id', $online_users['online_users']),
-			'ORDER BY'	=> 'u.username_clean ASC',
+			'ORDER_BY'	=> 'u.username_clean ASC',
 		);
 
 		/**