diff --git a/addons/web_calendar/static/src/js/web_calendar.js b/addons/web_calendar/static/src/js/web_calendar.js
index 70a46143aec..e3cc6e0e8d4 100644
--- a/addons/web_calendar/static/src/js/web_calendar.js
+++ b/addons/web_calendar/static/src/js/web_calendar.js
@@ -50,6 +50,9 @@ openerp.web_calendar = function(instance) {
             dayNames: moment.weekdays(),
             dayNamesShort: moment.weekdaysShort(),
             firstDay: moment._locale._week.dow,
+            weekNumberCalculation: function(date) {
+                return moment(date).week();
+            },
             weekNumbers: true,
             axisFormat : shortTimeformat.replace(/:mm/,'(:mm)'),
             timeFormat : {