On Thu, 18 Dec 2025 at 16:41, Christos Zoulas via tz <tz@iana.org> wrote:
Looks like this changed recently:

So, I guess this is fine now and NetBSD is broken.

It was undefined in POSIX.1-2001:
https://pubs.opengroup.org/onlinepubs/000095399/functions/fflush.html

But well-defined in POSIX.1-2008:
https://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html

So "recently" is at least 17 years ago :-)