diff --git a/htdocs/theme/md/style.css.php b/htdocs/theme/md/style.css.php
index 1681c48e4e1..9d7f7b76dd4 100644
--- a/htdocs/theme/md/style.css.php
+++ b/htdocs/theme/md/style.css.php
@@ -48,7 +48,7 @@ if (defined('THEME_ONLY_CONSTANT')) return;
 session_cache_limiter('public');
 
 
-require_once '../../main.inc.php';
+require_once __DIR__.'/../../main.inc.php'; // __DIR__ allow this script to be included in custom themes
 require_once DOL_DOCUMENT_ROOT.'/core/lib/functions2.lib.php';
 
 // Load user to have $user->conf loaded (not done into main because of NOLOGIN constant defined)