@mflatt trying to compile your Chez master, I get: Exception in $uncprep: unexpected record #[#{primref a0xltlrcpeygsahopkplcn-2} optimize-level 34 (0 1)]

(er, though, I wonder if my currently installed Chez is the problem here…)

Are you in a fresh checkout, or one where you built before?

built before, though I just updated my mflatt-master branch to your master

…or I just needed to do a distclean instead of a clean

Yes, that’s probably it