diff --git a/phpBB/includes/functions.php b/phpBB/includes/functions.php
index 06de40a764..c4be5330bd 100644
--- a/phpBB/includes/functions.php
+++ b/phpBB/includes/functions.php
@@ -1518,7 +1518,7 @@ function get_unread_topics($user_id = false, $sql_extra = '', $sql_sort = '', $s
 	if ($config['load_db_lastread'] && $user->data['is_registered'])
 	{
 		// Get list of the unread topics
-		$last_mark = $user->data['user_lastmark'];
+		$last_mark = (int) $user->data['user_lastmark'];
 
 		$sql_array = array(
 			'SELECT'		=> 't.topic_id, t.topic_last_post_time, tt.mark_time as topic_mark_time, ft.mark_time as forum_mark_time',
@@ -1537,10 +1537,11 @@ function get_unread_topics($user_id = false, $sql_extra = '', $sql_sort = '', $s
 			),
 
 			'WHERE'			=> "
+				 t.topic_last_post_time > $last_mark AND
 				(
 				(tt.mark_time IS NOT NULL AND t.topic_last_post_time > tt.mark_time) OR
 				(tt.mark_time IS NULL AND ft.mark_time IS NOT NULL AND t.topic_last_post_time > ft.mark_time) OR
-				(tt.mark_time IS NULL AND ft.mark_time IS NULL AND t.topic_last_post_time > $last_mark)
+				(tt.mark_time IS NULL AND ft.mark_time IS NULL)
 				)
 				$sql_extra
 				$sql_sort",