I ended up pushing a patch [1] for this as part of [2]. This has now
been released by upstream, so the change doesn't exist in the Guix
codebase any longer (the package was updated in [3]).

1: e61f092c877da5a9dc5dcdd82690bd3c191769e1
https://git.savannah.gnu.org/cgit/guix.git/commit/?id=e61f092c877da5a9dc5dcdd82690bd3c191769e1

2: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=32303

3: 7bb7920f64a871eadd8e76687f72673ef2298746
https://git.savannah.gnu.org/cgit/guix.git/commit/?id=7bb7920f64a871eadd8e76687f72673ef2298746