--- a/devtools/test/unittest_testlib.py	Mon Sep 14 18:12:44 2015 +0200
+++ b/devtools/test/unittest_testlib.py	Mon Sep 14 18:10:20 2015 +0200
@@ -17,10 +17,10 @@
 # with CubicWeb.  If not, see <http://www.gnu.org/licenses/>.
 """unittests for cw.devtools.testlib module"""
 
-from cStringIO import StringIO
-from io import BytesIO
+from io import BytesIO, StringIO
+from unittest import TextTestRunner
 
-from unittest import TextTestRunner
+from six import PY2
 
 from logilab.common.testlib import TestSuite, TestCase, unittest_main
 from logilab.common.registry import yes
@@ -52,7 +52,7 @@
 class WebTestTC(TestCase):
 
     def setUp(self):
-        output = StringIO()
+        output = BytesIO() if PY2 else StringIO()
         self.runner = TextTestRunner(stream=output)
 
     def test_error_raised(self):