In iOS 9, there’s a new feature called Wi-Fi assist. When you’re using a bad Wi-Fi connection, it switches over to cellular data. If you have an unlimited data plan, it’s no big deal. But if you do have a data ceiling, you may unknowingly blow past your limit, and that can cost money.

Here’s how to turn on and turn off Wi-Fi assist in iOS 9.

Access Wi-Fi Assist setting

1. Tap the Settings app to launch it.
2. Tap Cellular.
3. Scroll all the way to the bottom, past the list of apps that use cellular data.
4. You should find a setting for Wi-Fi Assist. You can switch it on or off.