Unlear error message parsing incorrectly formed A-R field

First I'd like to say this is a great library, thanks!

I just tried it parsing a DMARC header of an email sent from hotmail.com -> gmail.com which resulted in the following headers:

Authentication-Results: mx.google.com;
       dkim=pass <email address hidden> header.b=GNp0w69I;
       spf=pass (google.com: domain of <email address hidden> designates 40.92.5.38 as permitted sender) <email address hidden>;
       dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=hotmail.com

authentication-results: thehesiod.com; dkim=none (message not signed)
 header.d=none;thehesiod.com; dmarc=none action=none header.from=hotmail.com;

The "Authentication-Results" header parses fine, but the "authentication-results" header yields:

  File "/usr/local/lib/python3.5/site-packages/authres/core.py", line 553, in _parse_methodspec
    raise SyntaxError('Expected "="', self._parse_text)
authres.core.SyntaxError: Syntax error: Expected "=" at: ; dmarc=none action=none header.from=hot...