Want to save money on your phone bill? Make sure you turn off the "autoplay" setting on Facebook videos.

Smartphone users are at risk of maxing out their data plans if they don't change this default setting in the Facebook (FB) app, which otherwise will automatically start streaming videos in the News Feed window.

The issue was flagged by consumer finance site MoneySavingExpert.com, which said it had "seen many complaints from people who have been stung with data bills after exceeding their monthly allowance and who believe it to be because of Facebook autoplaying videos."

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A Facebook spokesperson said the company "want[s] to make sure that videos consume as little data as possible, and that people can control when they play automatically."

The fix, fortunately, is an easy one. If you're an iPhone user, tap your "Settings" button and then scroll down and click "Facebook." From there, click "Settings," "Auto-play," and then choose "Wi-Fi only" or "Off."

On Android, bring up the Facebook app and go to your account settings. Click "App Settings," and then choose 'Auto-play only on Wi-Fi' or 'Off.'

Videos won't also won't play automatically provided you scroll past them.

If you think you've been hit with unfair data charges, contact your wireless carrier.