diff -r 6b3523f81f42 -r 26744ad37953 cubicweb/web/box.py
--- a/cubicweb/web/box.py	Fri Apr 05 17:21:14 2019 +0200
+++ b/cubicweb/web/box.py	Fri Apr 05 17:58:19 2019 +0200
@@ -20,8 +20,6 @@
 
 from cubicweb import _
 
-from six import add_metaclass
-
 from logilab.mtconverter import xml_escape
 from logilab.common.deprecation import class_deprecated
 
@@ -58,8 +56,7 @@
 
 # old box system, deprecated ###################################################
 
-@add_metaclass(class_deprecated)
-class BoxTemplate(View):
+class BoxTemplate(View, metaclass=class_deprecated):
     """base template for boxes, usually a (contextual) list of possible
     actions. Various classes attributes may be used to control the box
     rendering.