diff --git a/product/ERP5Form/Document/Preference.py b/product/ERP5Form/Document/Preference.py
index 9442d5bceaf20e0b0e14dfbbe8d851df736a970d..bd5def817f2487f8a1cf1d75111f7b6da4be3ea7 100644
--- a/product/ERP5Form/Document/Preference.py
+++ b/product/ERP5Form/Document/Preference.py
@@ -68,7 +68,7 @@ class Preference( Folder ):
     """Clear caches used by methods of this preference
     # TODO: clear different caches according to the preference priority
     """
-    clearCache(cache_factory_list='erp5_ui_short')
+    clearCache(cache_factory_list=('erp5_ui_short'),)
 
   def _edit(self, **kw):
     """edit and clear all caches"""