def revocation_date(self, value):
        """
        A datetime.datetime object of when the certificate was revoked, if the
        status is not "good" or "unknown".
        """

        if value is not None and not isinstance(value, datetime):
            raise TypeError(_pretty_message(
                '''
                revocation_date must be an instance of datetime.datetime, not %s
                ''',
                _type_name(value)
            ))

        self._revocation_date = value