diff --git a/product/ERP5/Document/Document.py b/product/ERP5/Document/Document.py
index 7ed4b06cf86b9f0e4344f1e315db1d09582fa788..a46ad9c32bcb154c35b5b3adbf1b0a014bee823c 100644
--- a/product/ERP5/Document/Document.py
+++ b/product/ERP5/Document/Document.py
@@ -290,6 +290,7 @@ class Document(DocumentExtensibleTraversableMixin, XMLObject, UrlMixin,
                     , PropertySheet.CategoryCore
                     , PropertySheet.DublinCore
                     , PropertySheet.Version
+                    , PropertySheet.Reference
                     , PropertySheet.Document
                     , PropertySheet.ExternalDocument
                     , PropertySheet.Url