The U.S. Transportation Security Administration (TSA) pocketed almost $1 million left behind by travellers at airport security checkpoints last year.

CNBC reported that TSA collected $867,812.39 in loose change and small bills left in bins and bowls at security screening gates in 2016. That’s up about  $102,000 from the amount of cash left behind in 2015.

Each year, travellers have left more money at TSA checkpoints, data shows, although the agency is at a loss for explanations other than to say that more people are travelling by air than ever before.

Among U.S. airports, travellers at John F. Kennedy International Airport left behind the most money, $70,615, followed by Los Angeles International Airport (about $45,000) and Dallas/Fort Worth International Airport (about $42,000).

By federal law, TSA can keep any unclaimed cash left at its checkpoints and use it for security-related purposes. In the past, the agency has used the money to expand the TSA Precheck program, for example.

What can you do to avoid leaving an unintentional “tip” for TSA? Put your small change in your shoe when passing through a security checkpoint, advises travel writer Ramsey Qubein. Other tips include putting your money in an outside pocket of your luggage or handbag, and placing loose change in the small, round bowl rather than the big bin when going through screening, where it’s less likely to be overlooked when you retrieve your belongings.