Watchdog - cannot set timeout 16 (errno = 22 = 'Invalid argument')

Seen that error before?
Possibly on a Raspberry Pi 2/3?

Google seems to have problems guiding you to the right solution, so here it is:

Add watchdog-timeout = 15 to your watchdog.conf file.

Why is that? The Broadcom BCM2835 Watchdog timer only supports 15 seconds timeout ;)