Lars Ingebrigtsen <larsi@gnus.org> writes:

> Robert Pluim <rpluim@gmail.com> writes:
>
>> This signals an error because at this point 'substr' is a line of the
>> Face header with a leading space. Any of Lars' messages will trigger it.
>
> I pushed a fix a couple of hours ago...

Thanks Robert for finding the failure and thanks Lars for responding so
quickly!

This is my bad for not properly testing for the folding whitespace
continuation in long header fields. While spaces are illegal characters
in base 64, which is what I was testing for, it makes sense to deal with
potential FWSP sequences first since this function is specifically for
Gnus.