diff --git a/product/ERP5Type/tests/ERP5TypeTestCase.py b/product/ERP5Type/tests/ERP5TypeTestCase.py
index 2c4f3a2c8fa8991fe987d4204798d48af176a4a4..f322751c55ccdc8410bc57dede959f14131e65bc 100644
--- a/product/ERP5Type/tests/ERP5TypeTestCase.py
+++ b/product/ERP5Type/tests/ERP5TypeTestCase.py
@@ -286,9 +286,9 @@ class ERP5TypeTestCaseMixin(ProcessingNodeTestCase, PortalTestCase):
       """Restore original Mail Host
       """
       cls = self.portal.MailHost.__class__
-      assert cls.__bases__[0] is DummyMailHostMixin
-      cls.__bases__ = cls.__bases__[1:]
-      pmc_init_of(cls)
+      if cls.__bases__[0] is DummyMailHostMixin:
+        cls.__bases__ = cls.__bases__[1:]
+        pmc_init_of(cls)
 
     def pinDateTime(self, date_time):
       # pretend time has stopped at a certain date (i.e. the test runs