diff --git a/product/ERP5/Document/BusinessTemplate.py b/product/ERP5/Document/BusinessTemplate.py
index 6556b36a623e81fb12c717659245c35e74fc1738..246557d949b73e6c61f239e467c8462fd709fe76 100644
--- a/product/ERP5/Document/BusinessTemplate.py
+++ b/product/ERP5/Document/BusinessTemplate.py
@@ -3625,7 +3625,9 @@ class PropertySheetTemplateItem(DocumentTemplateItem,
     property_sheet_tool = context.getPortalObject().portal_property_sheets
     property_sheet_id_set = set(property_sheet_tool.objectIds())
 
-    for class_id in migrate_object_dict:
+    # careful, that dictionary will change
+    class_id_list = migrate_object_dict.keys()
+    for class_id in class_id_list:
       # If the Property Sheet already exists in ZODB, then skip it,
       # otherwise it should not be needed anymore once the deletion
       # code of the filesystem Property Sheets is enabled