diff --git a/product/ERP5/ERP5Site.py b/product/ERP5/ERP5Site.py
index 90f3ef969b033cffc449b222d53094fc64a52e1b..1b74abbcd5b8941158cc0044498f4b10fec7bd1a 100755
--- a/product/ERP5/ERP5Site.py
+++ b/product/ERP5/ERP5Site.py
@@ -549,8 +549,12 @@ class ERP5Site ( CMFSite, FolderMixIn ):
       """
         Return List of category values to generate security groups.
       """
-      return self._getPortalGroupedCategoryList('assignment') or self._getPortalConfiguration('portal_assignment_base_category_list')
-
+      category_tuple = self._getPortalGroupedCategoryList('assignment') or self._getPortalConfiguration('portal_assignment_base_category_list')
+      category_list = []
+      if category_tuple not in (None, '', (), []):
+        category_list = [ x for x in category_tuple]
+      return category_list
+    
     security.declareProtected(Permissions.AccessContentsInformation, 'getDefaultModuleId')
     def getDefaultModuleId(self, portal_type):
       """