diff --git a/install-dev/upgrade/php/create_multistore.php b/install-dev/upgrade/php/create_multistore.php
index c09b2916b..d0ecbf7b8 100755
--- a/install-dev/upgrade/php/create_multistore.php
+++ b/install-dev/upgrade/php/create_multistore.php
@@ -29,7 +29,8 @@ require_once(_PS_INSTALLER_PHP_UPGRADE_DIR_.'add_new_tab.php');
 function create_multistore()
 {
 	$res = true;
-
+	if (!defined('_THEME_NAME_'))
+		define('_THEME_NAME_', 'default');
 	// @todo : use _PS_ROOT_DIR_
 	if (defined('__PS_BASE_URI__'))
 		$INSTALLER__PS_BASE_URI = __PS_BASE_URI__;