diff --git a/addons/base_calendar/base_calendar.py b/addons/base_calendar/base_calendar.py
index 7657e52cc6b..f7a67adae11 100644
--- a/addons/base_calendar/base_calendar.py
+++ b/addons/base_calendar/base_calendar.py
@@ -1417,13 +1417,14 @@ e.g.: Every other month on the last Sunday of the month for 10 occurrences:\
         @return: True
         """        
         #removing useless value
-        old_vals = self.read(cr, uid, ids[0] if type(ids) == list else ids, ['rrule'], context)
-        if not old_vals:
-            old_vals = {}
-        if not 'rrule' in old_vals:
-            old_vals["rrule"] = ""
-        if 'rrule' in vals and not vals['rrule'] and not old_vals['rrule']: 
-            del vals['rrule']
+        if type(ids) == int or (type(ids) == list and len(ids) > 0):
+            old_vals = self.read(cr, uid, ids[0] if type(ids) == list else ids, ['rrule'], context)
+            if not old_vals:
+                old_vals = {}
+            if not 'rrule' in old_vals:
+                old_vals["rrule"] = ""
+            if 'rrule' in vals and not vals['rrule'] and not old_vals['rrule']: 
+                del vals['rrule']
         
         if context is None:
             context = {}