diff --git a/phpBB/includes/functions_admin.php b/phpBB/includes/functions_admin.php
index 8e7048ef0f..1f3fe1c8e8 100644
--- a/phpBB/includes/functions_admin.php
+++ b/phpBB/includes/functions_admin.php
@@ -3003,6 +3003,8 @@ function tidy_database()
 	}
 	$db->sql_freeresult($result);
 
+	$db->sql_transaction('begin');
+
 	// Delete those rows from the acl tables not having listed the forums above
 	$sql = 'DELETE FROM ' . ACL_GROUPS_TABLE . '
 		WHERE ' . $db->sql_in_set('forum_id', $forum_ids, true);
@@ -3012,6 +3014,8 @@ function tidy_database()
 		WHERE ' . $db->sql_in_set('forum_id', $forum_ids, true);
 	$db->sql_query($sql);
 
+	$db->sql_transaction('commit');
+
 	$config->set('database_last_gc', time(), false);
 }