diff --git a/product/ERP5Type/tests/ERP5TypeTestCase.py b/product/ERP5Type/tests/ERP5TypeTestCase.py
index bbe2229c1252463fe7b88126466eeb842278abf5..be58b7efecc3cf685869091bf139dfb123c9c221 100644
--- a/product/ERP5Type/tests/ERP5TypeTestCase.py
+++ b/product/ERP5Type/tests/ERP5TypeTestCase.py
@@ -547,8 +547,13 @@ class ERP5TypeTestCaseMixin(ProcessingNodeTestCase, PortalTestCase):
 
     def failIfDifferentSet(self, a, b, msg=""):
       if not msg:
-        msg='%r != %r' % (a, b)
-      self.assertEqual(set(a), set(b), msg)
+        try:
+          from pprint import pformat
+        except ImportError:
+          msg='%r != %r' % (sorted(a), sorted(b))
+        else:
+          msg='\n%s\n!=\n%s' % (pformat(sorted(a)), pformat(sorted(b)))
+      self.assertEquals(set(a), set(b), msg)
     assertSameSet = failIfDifferentSet
 
     def assertHasAttribute(self, obj, attribute, msg=None):