diff --git a/phpBB/develop/mysql_upgrader.php b/phpBB/develop/mysql_upgrader.php
index 5a7034b45c..70c8173a32 100644
--- a/phpBB/develop/mysql_upgrader.php
+++ b/phpBB/develop/mysql_upgrader.php
@@ -21,6 +21,7 @@
 die("Please read the first lines of this script for instructions on how to enable it");
 
 define('IN_PHPBB', true);
+$phpbb_root_path = (defined('PHPBB_ROOT_PATH')) ? PHPBB_ROOT_PATH : './';
 $phpEx = substr(strrchr(__FILE__, '.'), 1);
 include($phpbb_root_path . 'common.' . $phpEx);