diff --git a/htdocs/core/js/datepicker.js.php b/htdocs/core/js/datepicker.js.php
index 6cd3233b494..5295fae667d 100644
--- a/htdocs/core/js/datepicker.js.php
+++ b/htdocs/core/js/datepicker.js.php
@@ -127,7 +127,7 @@ jQuery(function($){
 		"'".$langs->trans("ShortSaturday")."'" ?>],
 		weekHeader: '<?php echo $langs->trans("Week"); ?>',
 		dateFormat: '<?php echo $langs->trans("FormatDateShortJQuery"); ?>',
-        firstDay: <?php echo $conf->global->MAIN_START_WEEK; ?>,
+        firstDay: <?php echo (isset($conf->global->MAIN_START_WEEK)?$conf->global->MAIN_START_WEEK:'1'); ?>,
         isRTL: <?php echo ($langs->trans("DIRECTION")=='rtl'?'true':'false'); ?>,
 		showMonthAfterYear: false,  // TODO add specific to country
 		yearSuffix: ''				// TODO add specific to country