Hey, So I've found another case of tricky decodings. I've been looking at the first email in this mbox file [1]. The From header is: From: =?UTF-8?Q?Ludovic_Court=E8s?= 1: https://lists.gnu.org/archive/mbox/guix-commits/2016-01 This seems to trip up guile-email within the decode-mime-encoded-word function, the bytevector returned by q-encoding-decode doesn't work with bytevector->string. I'm still not exactly sure why, some experimenting shows that the following decodes to what I guess is the intended text: Ludovic_Court=C3=A8s Similarly to the recent changes, specifying 'substitute as the third argument to bytevector->string at least avoids crashing in this case. Any thoughts? Chris