Apple’s iOS 9 software is already installed on well over 50% of existing devices, according to what Apple revealed in the first weekend after releasing the operating system. The new iOS version brings over a slew of improvements — though it doesn’t necessarily make older devices faster — as Apple focused mainly on performance gains rather than flashy new features.

Even so, there are plenty neat tricks available in iOS 9, including 3D Touch (only on iPhone 6s series), a smarter Siri and improved battery life. But there’s also one awesome feature that can turn out to be a nightmare for users.

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Called Wi-Fi Assist, the iOS 9 feature is enabled by default and it’s supposed to make sure that you’re getting a decent Wi-Fi experience. That means instantly switching to cellular data when Wi-Fi is spotty. For most users, that isn’t a problem, especially if they’re on large plans, or if they’re not consuming lots and lots of data by streaming video and music.

However, as Quartz explains, Wi-Fi Assist can turn out to be quite a data hog, as the device will continually try to supplement weaker Wi-Fi performance with carrier data.

The new feature can be turned off quickly — and you should do it whenever you’re roaming, or if you have dependable Wi-Fi networks at home and work. To do so, just go to Settings, then Cellular, and scroll down to the bottom to see if Wi-Fi Assist is turned on.

The blog says that the increased data consumption is not a bug, and Apple is aware of the issue — if you can call it an issue. Therefore you’ll have to fix it yourself to avoid unexpected data usage and get back to your regular monthly data consumption.

Chris Smith started writing about gadgets as a hobby, and before he knew it he was sharing his views on tech stuff with readers around the world. Whenever he's not writing about gadgets he miserably fails to stay away from them, although he desperately tries. But that's not necessarily a bad thing.