diff --git a/addons/web_calendar/static/src/js/web_calendar.js b/addons/web_calendar/static/src/js/web_calendar.js
index 51827c27e3c..18cca729b56 100644
--- a/addons/web_calendar/static/src/js/web_calendar.js
+++ b/addons/web_calendar/static/src/js/web_calendar.js
@@ -54,7 +54,7 @@ function get_fc_defaultOptions() {
         monthNamesShort: moment.monthsShort(),
         dayNames: moment.weekdays(),
         dayNamesShort: moment.weekdaysShort(),
-        firstDay: moment._locale._week.dow,
+        firstDay: moment()._locale._week.dow,
         weekNumberCalculation: function(date) {
             return moment(date).week();
         },