Citing safety concerns, Southwest Airlines will no longer allow passengers to charge devices with a power bank stowed inside a carry-on bag—going further than current FAA guidance.

Portable chargers and power banks might be useful additions to your carry-on luggage, but they’re also a potential fire risk. Now Southwest Airlines is tightening rules around their use on board aircraft.

The carrier will require passengers to keep lithium batteries visible while in use in order to allow flight crews to respond more quickly in case one catches fire.