--- a/src/mailman/core/runner.py	2014-04-23 14:29:53.000000000 +0200
+++ b/src/mailman/cure/runner.py	2014-06-24 20:37:22.573384698 +0200
@@ -25,6 +25,7 @@ __all__ = [
     ]
 
 
+import email
 import time
 import signal
 import logging
@@ -40,6 +41,7 @@ from mailman.config import config
 from mailman.core.i18n import _
 from mailman.core.logging import reopen
 from mailman.core.switchboard import Switchboard
+from mailman.email.message import Message
 from mailman.interfaces.languages import ILanguageManager
 from mailman.interfaces.listmanager import IListManager
 from mailman.interfaces.runner import IRunner, RunnerCrashEvent
@@ -236,6 +238,8 @@ class Runner:
         # will be the list's preferred language.  However, we must take
         # special care to reset the defaults, otherwise subsequent messages
         # may be translated incorrectly.
+        if (not isinstance(msg, Message)):
+            msg = email.message_from_string(msg.as_string(), Message)
         if mlist is None:
             language_manager = getUtility(ILanguageManager)
             language = language_manager[config.mailman.default_language]