diff --git a/addons/calendar/calendar.py b/addons/calendar/calendar.py
index 3e714243641..75b79922c5a 100644
--- a/addons/calendar/calendar.py
+++ b/addons/calendar/calendar.py
@@ -1349,7 +1349,7 @@ class calendar_event(osv.Model):
             data['rrule_type'] = 'monthly'
 
         if r._bymonthday:
-            data['day'] = r._bymonthday[0]
+            data['day'] = list(r._bymonthday)[0]
             data['month_by'] = 'date'
             data['rrule_type'] = 'monthly'