As airlines charge fees for more and more services, most people will look to save a couple bucks wherever they can. And it turns out that one place passengers can save money is alcohol.

There’s a little loophole used by JetBlue that allows passengers to drink alcohol they’ve brought onboard the plane.

Technically, according to FAA regulations, passengers can bring alcohol onboard — they just can’t open it themselves.

FAA rules state that only “the certificate holder operating the airline” is allowed to open and serve alcoholic beverages on board. If a passenger wants a drink of their own alcohol on a JetBlue flight, they must ask a flight attendant to serve them.

Although it may seem like a minor technicality, it’s a pretty important one. Because of well-documented issues with intoxicated passengers on planes, it’s part of the flight attendant’s duties to assess each drinking passenger’s sobriety levels. A flight attendant can stop serving at any time — even if a passenger brought their own alcohol and has a full bottle left.