A wealthy businessman is suing a Vegas casino, saying that he was too blackout for blackjack.

Fifty-two-year-old Mark Johnston dropped into the Downtown Grand casino to play some high-stakes pai gao poker and blackjack over Super Bowl weekend, dropping a cool half-million in the process.

But Johnston, who apparently "made his fortune" in car dealerships and real estate, says it's the Downtown Grand's problem—not his—because he was a sloppy, blackout drunk before he ever sat down to gamble.

He has been a Las Vegas regular for three decades, and says he came to the Grand during Super Bowl weekend at the invitation of the casino. He traveled with his girlfriend, but did most of his gambling alone. He drank in the limousine from the Las Vegas airport to the Grand on that Thursday and drank more during dinner with friends. The suit alleges that the Grand comped him dozens of drinks while he gambled away hundreds of thousands of dollars.

Allowing drunk patrons to gamble and serving obviously intoxicated patrons are both illegal under Nevada law. Johnston's lawyer says his client's story is bolstered by surveillance video and eyewitness testimony.

The Las Vegas Gaming Control Board is investigating.

[image via Shutterstock]