diff --git a/addons/base_calendar/base_calendar.py b/addons/base_calendar/base_calendar.py
index a735de4b823..694b89f34ad 100644
--- a/addons/base_calendar/base_calendar.py
+++ b/addons/base_calendar/base_calendar.py
@@ -1559,7 +1559,8 @@ true, it will allow you to hide the event alarm information without removing it.
                     # Remove one of the recurrent event
                     date_new = time.strftime("%Y%m%dT%H%M%S", \
                                  time.strptime(date_new, "%Y%m%d%H%M%S"))
-                    res = self.write(cr, uid, event_id, {'exdate': date_new})
+                    exdate = (record['exdate'] and (record['exdate'] + ',')  or '') + date_new
+                    res = self.write(cr, uid, event_id, {'exdate': exdate})
                 else:
                     res = super(calendar_event, self).unlink(cr, uid, event_id)
                     self.pool.get('res.alarm').do_alarm_unlink(cr, uid, event_id, self._name)