I've released python-gssapi version 0.6.1 a couple of days ago, which contains the new [subclasses of GSSException for BadSignature](http://pythonhosted.org/python-gssapi/api/gssapi.html#module-gssapi.error), etc. So I'd recommend requiring at least that version. That'll fix the problems with installation on Py3 as well, as that was fixed in 0.6.0.