A loophole in a United Nations charter has allowed Dennis Hope to sell plots on the moon for more than 30 years.

In the early 1980s, Hope, then unemployed for about a year, thought he’d be a good property owner and could make a living by managing real estate. He looked out the window and saw more unclaimed property than he could possibly fathom—the moon. He remembered a tidbit from a political science course he took in college—the 1967 United Nations Outer Space Treaty said no country could own the moon, but it says nothing about individuals.

Hope wrote a letter to the United Nations saying the moon was his and asked the group to come up with a legal reason why an individual could not claim ownership of the moon.

He never heard back.

“I sent the United Nations a declaration of ownership detailing my intent to subdivide and sell the moon and have never heard back,” he says. “There is a loophole in the treaty—it does not apply to individuals.”

Since then, he’s sold more than 611 million acres of land on the moon. Individual, one-acre lots sell for $19.95 ($36.50 after a “lunar tax” and shipping and handling of the deed) and there are discounts for larger plots. He once sold a “country-sized” plot of land—2.66 million acres—for $250,000. He’s sold plots on the moon to three former presidents (George H.W. Bush, Jimmy Carter and Ronald Reagan). He’s president of the Galactic Government, a democratic republic that represents landowners on the moon and some of his other properties (he claimed Mercury, Mars, Venus, Jupiter’s moon Io, and Pluto while he was at it). Customers can buy the entirety of Pluto for $250,000.

According to Tanja Masson-Zwaan, president of the International Institute of Space Law, the United Nations never responded because the treaty applies to both countries and its citizens, she told National Geographic.