I get this with a clean build from today's sources, no options:

Copying /p/i386-current/image/usr/mdec/boot to boot
Creating USTAR.volsize.4540
Copying /p/i386-current/obj/usr/src/distrib/i386/floppies/instkernel/netbsd-RESCUE_TINY.gz
 to netbsd
Creating rescue-tiny1.fs from: boot USTAR.volsize.4540 netbsd
PAX=/p/i386-current/tools/bin/nbpax sh /usr/src/distrib/common/buildfloppies.sh
 -i "/p/i386-current /tools/bin/nbinstallboot  -mi386 @IMAGE@
 /p/i386-current/image/usr/mdec/bootxx_ustarfs" -p  -m 1 -s .fs
 rescue-tiny 2400 boot USTAR.volsize.4540 netbsd
Running instboot: /p/i386-current/tools/bin/nbinstallboot -mi386 floppy.25259.tar
 /p/i386-current/image/usr/mdec/bootxx_ustarfs
buildfloppies.sh: Image is 16384 bytes (16 KB) too big to fit on 1 disk

*** Failed target:  rescue-tiny1.fs
*** Failed command: PAX=/p/i386-current/tools/bin/nbpax sh
/usr/src/distrib/common/buildfloppies.sh
 -i "/p/i386-current/tools/bin/nbinstallboot -mi386 @IMAGE@
 /p/i386-current/image/usr/mdec/bootxx_ustarfs" -p -m 1 -s .fs
 rescue-tiny 2400 boot USTAR.volsize.4540 netbsd
*** Error code 1

Stop.
nbmake: stopped in /usr/src/distrib/i386/floppies/rescue-tiny

[and so on]

Funny thing is, it worked fine just a couple of days ago.

Should we bump the size of the single floppies to 1440? Does anyone
still have a working 1.2 Mb floppy drive? (I actually have one of
those, but it's on a system that can't boot from the second floppy
drive, and I'm not even sure it still works at all, as it's been a
few years since I've come across any media for it.)

Frederick