diff --git a/install/db/133-database.php b/install/db/133-database.php
new file mode 100644
index 000000000..a69bbb9ef
--- /dev/null
+++ b/install/db/133-database.php
@@ -0,0 +1,35 @@
+<?php
+// +-----------------------------------------------------------------------+
+// | Piwigo - a PHP based photo gallery                                    |
+// +-----------------------------------------------------------------------+
+// | Copyright(C) 2008-2012 Piwigo Team                  http://piwigo.org |
+// | Copyright(C) 2003-2008 PhpWebGallery Team    http://phpwebgallery.net |
+// | Copyright(C) 2002-2003 Pierrick LE GALL   http://le-gall.net/pierrick |
+// +-----------------------------------------------------------------------+
+// | This program is free software; you can redistribute it and/or modify  |
+// | it under the terms of the GNU General Public License as published by  |
+// | the Free Software Foundation                                          |
+// |                                                                       |
+// | This program is distributed in the hope that it will be useful, but   |
+// | WITHOUT ANY WARRANTY; without even the implied warranty of            |
+// | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU      |
+// | General Public License for more details.                              |
+// |                                                                       |
+// | You should have received a copy of the GNU General Public License     |
+// | along with this program; if not, write to the Free Software           |
+// | Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, |
+// | USA.                                                                  |
+// +-----------------------------------------------------------------------+
+
+defined('PHPWG_ROOT_PATH') or die('Hacking attempt!');
+
+$upgrade_description = '#categories.site_id default value.';
+
+$query = 'ALTER TABLE '.CATEGORIES_TABLE.' CHANGE site_id site_id tinyint(4) unsigned default NULL';
+pwg_query($query);
+
+$query = 'UPDATE '.CATEGORIES_TABLE.' SET site_id=NULL WHERE dir IS NULL';
+pwg_query($query);
+
+echo "\n".$upgrade_description."\n";
+?>
\ No newline at end of file
diff --git a/install/piwigo_structure-mysql.sql b/install/piwigo_structure-mysql.sql
index cde461bcd..0a0d9e611 100644
--- a/install/piwigo_structure-mysql.sql
+++ b/install/piwigo_structure-mysql.sql
@@ -28,7 +28,7 @@ CREATE TABLE `piwigo_categories` (
   `dir` varchar(255) default NULL,
   `rank` smallint(5) unsigned default NULL,
   `status` enum('public','private') NOT NULL default 'public',
-  `site_id` tinyint(4) unsigned default '1',
+  `site_id` tinyint(4) unsigned default NULL,
   `visible` enum('true','false') NOT NULL default 'true',
   `representative_picture_id` mediumint(8) unsigned default NULL,
   `uppercats` varchar(255) NOT NULL default '',