diff --git a/phpBB/viewtopic.php b/phpBB/viewtopic.php
index 50481302e6..dfee8fd2f7 100644
--- a/phpBB/viewtopic.php
+++ b/phpBB/viewtopic.php
@@ -388,7 +388,7 @@ if (!isset($topic_tracking_info))
 $limit_days = array(0 => $user->lang['ALL_POSTS'], 1 => $user->lang['1_DAY'], 7 => $user->lang['7_DAYS'], 14 => $user->lang['2_WEEKS'], 30 => $user->lang['1_MONTH'], 90 => $user->lang['3_MONTHS'], 180 => $user->lang['6_MONTHS'], 365 => $user->lang['1_YEAR']);
 
 $sort_by_text = array('a' => $user->lang['AUTHOR'], 't' => $user->lang['POST_TIME'], 's' => $user->lang['SUBJECT']);
-$sort_by_sql = array('a' => array('u.username_clean', 'p.post_id'), 't' => 'p.post_time', 's' => array('p.post_subject', 'p.post_id'));
+$sort_by_sql = array('a' => array('u.username_clean', 'p.post_id'), 't' => array('p.post_time', 'p.post_id'), 's' => array('p.post_subject', 'p.post_id'));
 $join_user_sql = array('a' => true, 't' => false, 's' => false);
 
 $s_limit_days = $s_sort_key = $s_sort_dir = $u_sort_param = '';