diff --git a/addons/calendar/calendar.py b/addons/calendar/calendar.py
index 427f515ffd0..5da9104b6a8 100644
--- a/addons/calendar/calendar.py
+++ b/addons/calendar/calendar.py
@@ -1759,9 +1759,10 @@ class mail_message(osv.Model):
         '''
         convert the search on real ids in the case it was asked on virtual ids, then call super()
         '''
+        args = list(args)
         for index in range(len(args)):
             if args[index][0] == "res_id" and isinstance(args[index][2], basestring):
-                args[index][2] = get_real_ids(args[index][2])
+                args[index] = (args[index][0], args[index][1], get_real_ids(args[index][2]))
         return super(mail_message, self).search(cr, uid, args, offset=offset, limit=limit, order=order, context=context, count=count)
 
     def _find_allowed_model_wise(self, cr, uid, doc_model, doc_dict, context=None):
@@ -1781,9 +1782,10 @@ class ir_attachment(osv.Model):
         '''
         convert the search on real ids in the case it was asked on virtual ids, then call super()
         '''
+        args = list(args)
         for index in range(len(args)):
             if args[index][0] == "res_id" and isinstance(args[index][2], basestring):
-                args[index][2] = get_real_ids(args[index][2])
+                args[index] = (args[index][0], args[index][1], get_real_ids(args[index][2]))
         return super(ir_attachment, self).search(cr, uid, args, offset=offset, limit=limit, order=order, context=context, count=count)
 
     def write(self, cr, uid, ids, vals, context=None):