diff --git a/Lib/test/test_mailbox.py b/Lib/test/test_mailbox.py
index ffeeb3e..7dc5216 100644
--- a/Lib/test/test_mailbox.py
+++ b/Lib/test/test_mailbox.py
@@ -519,6 +519,7 @@
         class FakeMessage(mailbox.MaildirMessage):
             pass
         box = mailbox.Maildir(self._path, factory=FakeMessage)
+        box.colon = self._box.colon
         msg2 = box.get_message(key)
         self.assert_(isinstance(msg2, FakeMessage))