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 TSA already bans rechargeable and non-rechargeable lithium batteries for phones and laptops from checked baggage. Carry-on baggage is fine, but Southwest Airlines will soon require those chargers to be outside of all bags and visible while in use during the duration of the flight.

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.