Burger King is running a promotional campaign this Christmas where it will swap an unwanted present for a burger.

On Boxing Day (December 26th 2016), selected Burger King outlets will let customers bring in gifts of any value to exchange for one free burger. All presents received will be donated to a local charity.

The catch? The outlets participating in the promotion are one restaurant in Miami, Florida, one in London, UK, and an unspecified number in Brazil.

In London, the outlet involved is the Burger King restaurant in Leicester Square. Unwanted gifts must be unused and, a Burger King spokesperson says, accepted only at the discretion of employees at participating outlets. The first 500 qualifying gifts brought in to the Leicester Square outlet between 10.00am and 6.00pm on Boxing Day will be swapped for a flame-grilled Whopper sandwich.

People unable to make it to a participating restaurant with their unwanted gifts on December 26th can still participate in the promotion by posting a picture on social media of their questionable presents with the hashtag #WhopperExchange. A certain number will be rewarded with a gift card which they can redeem for a free Whopper at their local restaurant.

Renato Rossi, Chief Marketing Officer for Burger King UK, says: “At BURGER KING restaurants, we are always looking for ways to surprise our fans, no matter if they were good or naughty. The Whopper Exchange will offer our guests the chance to basically get a flame-grilled gift in exchange for an unwanted one. Because this holiday season, we want everyone to receive something they will love.”