What happens with FreeBSD pkg and ports ends up with a corrupted database?

This happens from time to time, here’s how it was solved:

# pkgdb -F
—> Checking the package registry database
[Updating the pkgdb in /var/db/pkg ... /var/db/pkg/pkgdb.db: unexpected file type or format -- Invalid argument; rebuild needed] [Rebuilding the pkgdb [...]