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The actor only just turned 18 a few months back, plus she's in a relationship with Jake Bongiovi, son of rocker Jon Bon Jovi, but still, it's always good to have a contingency plan.
In a recent interview, Brown - who plays Eleven in the hit Netflix series - appeared alongside 17-year-old Noah Schnapp - aka Will Byers - and they opened up about their marriage pact.
"We said if we're not married by 40, we'll get married together because we'd be good roomies," she told MTV News.
As well as being predicated on them both being single in a good 20+ years, Brown also pointed out a few other important conditions.
She continued: "Completely platonically, we would still be really good roomies.
"No kids, though, because I could not deal with a child of yours... yeah, that's my dealbreaker too.
"Yeah, no kids at all. Only dogs... and separate bedrooms, for sure - my God, you're so messy."
Hmmm, not sure this sounds like it would be the best marriage in the world, but they've got two decades to do better.
However, whether or not they ever get married, it sounds like they've built a friendship that will stand the test of time.
The sci-fi drama that brought them together was first released back in 2016, meaning they've grown up alongside each other, both on and off the screen.
Brown said: "Noah and I have been friends for eight years, I've known you since I was 10.
"We have built such a friendship together, I feel like. And you're also one of the longest friends I've ever had, I don't know if you know that, but I didn't grow up in school so I didn't have any friends from my childhood, so you really are one of those people for me."
She added: "Something I do want to add is that, being a young girl in the industry, it's really hard when you are constantly surrounded by male energy.
"Something that Noah has always done so well is make me feel so comfortable, so empowered, and he is an amazing co-star to riff off of.
"He's always been my biggest supporter cheering me on and for that, especially in this day and age, I think it's really nice to have boys like that. Boys who support girls."