In Iceland, everybody is related. Okay, technically everybody everywhere is related, but in Iceland people are way more related than they are in, say, the United States. The population of Iceland today is about 320,000, and, accord to the genealogy website islendingabok.is, the whole population of native Icelanders derives from a single family tree. As the Icelandic news site News of Iceland says, that’s enough people that not everyone knows each other, but few enough to mean that two Icelanders who are dating might actually be cousins.

This is a common enough problem for Icelanders that there is now an app to help people avoid dating their close relatives. The app uses that same genealogy website to look you, and your potential date, up, and confirm that you’re not actually related. News of Iceland:

Three engineers made an app for the ‘Íslendingabók‘ database. People can now easily, and on the go, look up how they are related to other Icelanders. And a precious feature, using the bump technology, allows people that meet to just bump their phones together, to instantly see if they are too related to take things any further. The engineers’ slogan for this feature was: “Bump the app before you bump in bed”.

You might be thinking that there is no way that Icelanders really have this problem. But they do. In fact, in 2007, the Iceland Review Online ran a story about this very conundrum. The journalist writes that she made sure that her and her boyfriend were not related. But her brother begged to differ:

The next day there was an email from him waiting in my inbox. I opened it and discovered a list of names and dates of birth – a family tree. I recognized some of the names and soon realized that this was a list of my ancestors and my boyfriend’s ancestors, all the way back to the 18th century. Apparently we share a great-great-great-great-great-great-great grandmother, whose name was Gudrún Einarsdóttir. She was born in 1742 and died in 1784. I derive from her son, Einar (born 1762), and my boyfriend from her daughter, Hallfrídur (born 1770).

Another story, in the Global Post, explains that this story isn’t uncommon in Iceland at all:

Most Icelanders have heard a story of somebody, who knew somebody, who found out a bit late in the game that the subject of their romance is actually an estranged cousin. Elin Edda says it happened to her friend. “She really liked this guy and then found out they had the same great-grandparents,” she says. “It really freaked her out and she broke it off. It was just too weird.”

If Edda had had this app, however, she could have avoided that whole problem. So while in many countries people are using their iPhones to maximize their dates, in Iceland, more isn’t always better, because the more you date, the more likely you are to date your cousin.

More from Smithsonian.com:

What We Know From the Icelandic Volcano

A lonely farm in Iceland