(NEXSTAR) – Shake Shack announced a special offer Thursday for its vaccinated customers across the country.

Starting Friday, anyone who has had the single shot Johnson & Johnson COVID-19 vaccine or at least one Moderna or Pfizer shot can show their vaccination card to receive a free side of fries.

There is a little fine print, however – to cash in on the deal you have to buy a burger or chicken sandwich, and the offer isn’t good at airports, stadiums and ballparks. And no, “I got my COVID-19 vaccine” stickers don’t count as proof of vaccination.

Creative, fry-loving Shake Shack customers may also be disappointed to learn that they can’t “borrow” vaccination cards from friends and family to get multiple free orders.

The offer is good from Friday, May 21 through Saturday, June 12.

See participating locations and additional information from Shake Shack.