diff --git a/addons/web/controllers/main.py b/addons/web/controllers/main.py
index b74efc9c452..16c245fc31a 100644
--- a/addons/web/controllers/main.py
+++ b/addons/web/controllers/main.py
@@ -1330,7 +1330,7 @@ class Export(http.Controller):
             fields['.id'] = fields.pop('id', {'string': 'ID'})
 
         fields_sequence = sorted(fields.iteritems(),
-            key=lambda field: field[1].get('string', ''))
+            key=lambda field: openerp.tools.ustr(field[1].get('string', '')))
 
         records = []
         for field_name, field in fields_sequence: