The Simpsons Tapped Out is one of many iOS games to include loot boxes.

Apple announced a sweeping revision to the guidelines for its App Store yesterday, which now includes a provision that loot boxes must be transparent about their odds.

“Apps offering ‘loot boxes’ or other mechanisms that provide randomized virtual items for purchase must disclose the odds of receiving each type of item to customers prior to purchase,” reads the new rule, which will affect the most popular games on iOS, including Hearthstone, The Simpsons Tapped Out, and Clash Royale.

Loot boxes, which have always been common in the world of iOS gaming, are virtual grab bags that can give players a host of items ranging from common to rare. Most of the time, you can buy these loot boxes not just for in-game currency but for real money, which has led some players to classify them as gambling—a label that the Entertainment Software Rating Board doesn’t acknowledge.

This news comes after a year full of controversy over loot boxes, which many players see as manipulative, predatory methods to get them to spend more money on games. Although many mobile games have always had them, loot boxes received renewed attention this year thanks to their inclusion in console games like Shadow of War and Star Wars Battlefront II. Rage over the latter game dominated its launch to the point where its publisher, EA, announced the day before release that it was temporarily removing all of Battlefront II’s microtransactions.

As rage over these practices gets louder and louder, Apple’s move is the first of what may be many steps that game publishers and distributors voluntarily take in an attempt to avoid regulation from outside bodies.