Straphangers, beware: some iPhone users who are swiping in with MetroCards are being double-charged at subway stations that use the MTA's new tap-and-go payment system.

The contactless payment option celebrated its five millionth tap this week, but, according to the MTA, some riders have been charged twice if "Express Transit" mode is enabled on their iPhone's Apple Pay and they swipe in with a MetroCard.

The MTA told NY1 that dozens of commuters have been hit with these additional charges and it was in touch with Apple to address the issue.

You make sure "Express Transit" mode is turned off on your iPhone by going to your settings under the "Wallet & Apple Pay" section.