Since Paddy and Patty are usually pronounced the same way, it hardly matters whether you’re wishing someone a “Happy St. Paddy’s Day!” or a “Happy St. Patty’s Day!” aloud. If you’re writing it out, however, only one is technically correct.

As Real Simple explains, Patrick is the Anglicized version of the Gaelic name Pádraig. Because St. Patrick’s Day is originally an Irish holiday—and Gaelic is a traditional Irish language—the right nickname is Paddy, rather than Patty. (Interestingly enough, St. Patrick himself wasn’t from Ireland, though he definitely did learn the language.)

“St. Patty’s Day” probably became popular in America because people heard "St. Paddy's Day" and assumed it was spelled with a t, like St. Patrick. It may seem like a small distinction, but it’s a major pet peeve for many an Irish person scrolling through social media come March 17—so much so that one enterprising citizen, Marcus Campbell, even founded a website in 2010 called PaddyNotPatty.com.

Patty is the diminutive of Patricia, or a burger, and just not something you call a fella,” Campbell writes on the site.

But before you text, tweet, or send a telegram with a jolly “Happy St. Paddy’s Day!” this year, you should know that the word Paddy has a bit of a contentious history. According to Merriam-Webster, it’s also sometimes used as a derogatory term for an Irish person—so if you’d rather forgo the nicknames altogether and just stick with “St. Patrick’s Day,” that’s fine, too.

Wondering what else you might not know about the shamrock-filled holiday? Find out 13 fascinating facts here.

[h/t Real Simple]