On Wednesday, Facebook (s fb) made a big change in the way that it manages content — and its approach to gun control: it announced via blog post that it would take measures to curb illegal gun sales Through Facebook and Instagram.

Gun sales are actually a thriving subsection of Facebook — gun enthusiasts show off their collections and even offer up their wares for sale (whether it’s through retail or personal ownership). But new rules, enforceable on both Facebook and Instagram, seek to stop illegal sales, ones that circumvent federal law and are believed to be responsible for many guns on the streets today.

The measures are pretty cut and dry:

• Users who post a photo of a “commonly regulated item” (which, in this case includes guns, but could be, say, marijuana for sale posted by a legal dispensary) will get a message by Facebook to remind them to…