diff --git a/client/modules/crm/src/views/calendar/calendar.js b/client/modules/crm/src/views/calendar/calendar.js
index 2b8f1e9cb9..22ba633896 100644
--- a/client/modules/crm/src/views/calendar/calendar.js
+++ b/client/modules/crm/src/views/calendar/calendar.js
@@ -386,6 +386,7 @@ Espo.define('crm:views/calendar/calendar', ['view', 'lib!full-calendar'], functi
                 timeFormat: this.getDateTime().timeFormat,
                 defaultView: this.mode,
                 weekNumbers: true,
+                weekNumberCalculation: 'ISO',
                 editable: true,
                 selectable: true,
                 selectHelper: true,