diff --git a/trytond/tests/test_tryton.py b/trytond/tests/test_tryton.py
index 9f732a1303..bc818fc7df 100644
--- a/trytond/tests/test_tryton.py
+++ b/trytond/tests/test_tryton.py
@@ -133,7 +133,8 @@ class ModuleTestCase(unittest.TestCase):
             tree = etree.fromstring(res['arch'])
 
             validator = etree.RelaxNG(etree=View.get_rng(res['type']))
-            validator.assert_(tree)
+            # Don't use assert_ because 2to3 convert to assertTrue
+            validator.assertValid(tree)
 
             tree_root = tree.getroottree().getroot()