diff --git a/openerp/osv/orm.py b/openerp/osv/orm.py
index b316b50e654..661201dc0e7 100644
--- a/openerp/osv/orm.py
+++ b/openerp/osv/orm.py
@@ -2679,7 +2679,7 @@ class BaseModel(object):
                     if interval == 'day':
                         display_format = 'dd MMMM YYYY' 
                     elif interval == 'week':
-                        display_format = 'w'
+                        display_format = "'W'w"
                     elif interval == 'month':
                         display_format = 'MMMM'
                     elif interval == 'quarter':