By Ethan Wolff-Mann
October 2, 2015
Prathan Chorruangsak—Shutterstock

If you’re subscribed to Apple Music or iTunes Match, you could find yourself saddled with some very unpleasant overage charges after updating to the new iOS 9 this month.

Among the changes Apple has made to the mobile operating system is a new setting that makes the device always stream music at the highest quality level, even when the music is being streamed via cellular data signals (as opposed to “free” wi-fi signals). Naturally, this can burn through data incredibly fast: Gigabytes in days, if you’re not careful.

To turn it off, go to “Settings” and scroll down to “Music.” Open that tab and make sure the “High Quality on Cellular” button is turned off. (If you have disabled “Use Cellular Data” for the Music app, none of this will be a problem for you.)

If you have a unlimited data plan grandfathered in, this won’t affect you, but for people on a limited data budget, it could make for a very unpleasant “you’ve reached your data limit” text just days into a billing cycle.

More: If You Upgraded to iOS 9, This Trick Will Save You from Data Overages

Happily, it doesn’t appear that this is the default setting, but people wanting some cellular data access for downloading and playing music may be inadvertently checking that box allowing the excess data.

This setting also presents an issue for iTunes Match users who already have music downloaded onto their phones. Even though the file is currently on the phone, the Music app can override that song and stream a higher quality version via cellular.

If you really do want quality at any cost outside of Wi-Fi range, then by all means, turn the “High Quality on Cellular” setting on! But the vast majority of us who ration our data will want it disabled.

Read next: Use this tool to find the best cellphone plan for you.

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