diff --git a/core/Constants.php b/core/Constants.php
index ecadf404d..3e958a0ea 100644
--- a/core/Constants.php
+++ b/core/Constants.php
@@ -122,6 +122,7 @@ if(!defined('TRUSTED_PROXY')) {
  */
 if(!isset($_SERVER['HTTP_HOST'])) {
 	// HTTP_HOST, REQUEST_PORT, SCRIPT_NAME, and PHP_SELF
+	global $_FILE_TO_URL_MAPPING;	
 	if(isset($_FILE_TO_URL_MAPPING)) {
 		$fullPath = $testPath = realpath($_SERVER['SCRIPT_FILENAME']);
 		while($testPath && $testPath != '/' && !preg_match('/^[A-Z]:\\\\$/', $testPath)) {