Xcode 9.3 on MacOS generates a stack fault when viewing a message

I just built 4fe6cfeb. The resulting mutt can load the index of an INBOX over IMAP, but as soon as I try to view a message, I get:

Fetching message... 0/69K (0%)/usr/local/bin/mutt: line 24: 20634 Abort trap: 6           mutt