A man walks into a bar in Belgium and the bartender says, “put your shoe in this basket.” It sounds like the start of a joke, but at least one bar in Belgium has started demanding that customers hand over one of their shoes whenever they order the house beer.

It’s not a gimmick — tourists keep stealing their glasses and it’s getting expensive. In Belgium, every beer has its own kind of glass, which often has a distinct shape and is stamped with the brewer’s or even the bar’s logo. Because of their uniqueness and keep-sakey appearance, many believe buying a beer entitles them to keep the glass as a souvenir.

This has frustrated bars and pubs across the country, who lose tens of thousands of Belgian beer glasses to treasure seekers every year. While some bars have installed expensive alarm systems and scanners at their doors, the Dulle Griet bar in Ghent is taking a lower-tech approach to prevent theft: ransom.

“Anyone who drinks our house beer must hand over their shoe,” Alex Devriendt told the Belgian newspaper Nieuwsblad. “We then put them in a basket that we put up against the ceiling. The basket has now become an attraction, but for us, it remains a guarantee. [The glasses] are quite expensive because we have them made especially for us”.

While demanding collateral for a beer might be effective for glassware, it seems that beer mugs aren’t the only thing tourists are after. “We have to supplement our inventory every day”, added Devriendt. “Tourists simply want a souvenir. Some even try to throw those old-fashioned billboards off my wall. Certainly, in the winter, a lot disappears, they have thick coats on. In the summer they can hide the loot less well”.

It remains to be seen if people will still favor a keepsake from the bar more than their shoes. At least locals will have an easier job at spotting the guilty parties: all they need to look for is someone walking around half barefoot.