Nearly one quarter of McDonald’s Filet-of-Fish sandwich sales take place during Lent, when many fast-food customers are abstaining from meat. That’s exactly what the McDonald’s operator who first put the cheese-topped sandwich on his menu had in mind back in 1962.

According to an account in Reader’s Digest, when Cincinnati McDonald’s franchise owner Lou Groen noticed that his heavily Catholic clientele was avoiding his restaurant on Fridays, he suggested to McDonald’s owner Ray Kroc that they add introduce a fish sandwich.

Kroc thought fried fish wouldn’t fly, but suggested offering customers the choice of a meat-free “Hula Burger” made of pineapple and cheese on a bun and Groen’s Filet-o-Fish. Whichever sandwich was more popular would earn a spot on the menu.

TIL McDonald's introduced a Pineapple burger in the 1960s called the Hula Burger. pic.twitter.com/YSg7Brd3xn — Ali 🤠🐴 (@Ink184) March 29, 2017

Needless to say, the fish sandwich won, and Groen’s restaurant thrived. Since then, the sandwich has been McDonald’s fixture, all year long.