--- a/web/views/__init__.py	Wed Sep 16 11:28:07 2015 +0200
+++ b/web/views/__init__.py	Wed Sep 16 13:57:21 2015 +0200
@@ -23,6 +23,8 @@
 import sys
 import tempfile
 
+from six import add_metaclass
+
 from rql import nodes
 from logilab.mtconverter import xml_escape
 from logilab.common.deprecation import class_deprecated
@@ -127,8 +129,8 @@
 
 
 
+@add_metaclass(class_deprecated)
 class TmpFileViewMixin(object):
-    __metaclass__ = class_deprecated
     __deprecation_warning__ = '[3.18] %(cls)s is deprecated'
     binary = True
     content_type = 'application/octet-stream'