diff --git a/mass_editing/mass_editing.py b/mass_editing/mass_editing.py
index 6ed0edba6..537015ac4 100644
--- a/mass_editing/mass_editing.py
+++ b/mass_editing/mass_editing.py
@@ -50,7 +50,7 @@ class mass_object(osv.osv):
                 for key, val in active_model_obj._inherits.items():
                     found_model_ids = model_obj.search(cr, uid, [('model', '=', key)])
                     if found_model_ids:
-                        model_ids += [found_model_ids[0]]
+                        model_ids.append(found_model_ids[0])
         return {'value': {'model_ids': [(6, 0, model_ids)]}}
 
     def create_action(self, cr, uid, ids, context=None):