CHICAGO (AP) — Chicago’s O’Hare and Midway international airports have installed boxes where travelers can dispose of recreational marijuana before they board their flights.

The cannabis amnesty boxes, as they’re called, were installed at each airport last week, just as legal marijuana sales began in Illinois. The Chicago Tribune reports the boxes are located just past the airports’ Transportation Security Administration checkpoints.

Chicago Police Department spokeswoman Maggie Huynh says that while it’s not illegal to have cannabis at the airport, possessing marijuana is still illegal under federal law.

She says the boxes give people an opportunity to ensure they won’t run into an issue when they land at their destination.