diff --git a/trytond/model/workflow.py b/trytond/model/workflow.py
index f8d54e283a..940eec9e48 100644
--- a/trytond/model/workflow.py
+++ b/trytond/model/workflow.py
@@ -33,7 +33,7 @@ class Workflow(object):
 
                 result = func(cls, filtered, *args, **kwargs)
                 if to_update:
-                    for record in to_update:
+                    for record in to_update.keys():
                         current_state = getattr(record, cls._transition_state)
                         if current_state != to_update[record]:
                             del to_update[record]