This bug was also present in Email::MIME::ContentType:
commit ae081fb576d8507efca4928116ad81efa756c723 (refs/pull/pull/9/head)
in https://github.com/rjbs/Email-MIME-ContentType.git
Our fix is shorter, but dependent on 5.10+ as our codebase
relies on Perl 5.10 features, anyways.