unknown encoding crashes qrunner

Certain messages encoded with gb2312 are causing qrunner to
crash. This is version 2.1.5. Here's the traceback:

Jun 16 12:17:47 2004 (16350) Uncaught runner exception:
unknown encoding: gb2312
Jun 16 12:17:48 2004 (16350) Traceback (most recent call last):
  File "/export/local/mailman/Mailman/Queue/Runner.py", line 111,
in _oneloop
    self._onefile(msg, msgdata)
  File "/export/local/mailman/Mailman/Queue/Runner.py", line 167,
in _onefile
    keepqueued = self._dispose(mlist, msg, msgdata)
  File "/export/local/mailman/Mailman/Queue/IncomingRunner.py",
line 130, in _dispose
    more = self._dopipeline(mlist, msg, msgdata, pipeline)
  File "/export/local/mailman/Mailman/Queue/IncomingRunner.py",
line 153, in _dopipeline
    sys.modules[modname].process(mlist, msg, msgdata)
  File "/export/local/mailman/Mailman/Handlers/CookHeaders.py",
line 74, in process
    prefix_subject(mlist, msg, msgdata)
  File "/export/local/mailman/Mailman/Handlers/CookHeaders.py",
line 262, in prefix_subject
    h.append(s, c)
  File "/export/local/mailman/pythonlib/email/Header.py", line 285,
in append
    s = s.encode(outcodec, errors)
LookupError: unknown encoding: gb2312

Jun 16 12:17:48 2004 (16350) SHUNTING:
1087397495.8902061+fc54fd2fa39a5ae96ee648333b6f1adf782a385
7

Here are the message headers:

From: =?GB2312?B?uePW3cfsyPA=?=
<email address hidden>
Content-Type: text/plain;charset="GB2312"
Content-Transfer-Encoding: 8bit

[http://sourceforge.net/tracker/index.php?func=detail&aid=974290&group_id=103&atid=100103]