SACRAMENTO, Calif. (AP) — Owners of certain firearms that are now illegal to buy under California’s expanded definition of assault weapons will have to register them in coming months in order to be grandfathered in.

The registration period starts Thursday and applies to gunowners who legally bought so-called bullet-button assault weapons. California lawmakers outlawed weapons with that feature in 2016. But those who bought them before the law took effect on Jan. 1, 2017, are still allowed to own them, so long as they register the weapons with the state.

It’s the second time the state has opened a registration window. Critics said it botched the first try in 2018.