Bitcoin buyers beware.

On Tuesday, Mike Novogratz — a former Fortress Investment Group trader who lately has been pumping the controversial cryptocurrency — warned there will be “wild crashes” in bitcoin, just as it crossed the $10,000 mark.

“This is going to become the biggest bubble of our lifetimes by a long shot,” Novogratz said at an industry conference in New York. “There will be wild crashes in it.”

The price of bitcoin has surged tenfold this year, making for one of the biggest run-ups in price for any asset ever.

Still, not everyone is impressed. Incoming Federal Reserve Chair Jerome Powell shrugged off the cryptocurrency craze in a Washington hearing, saying cryptocurrencies “just don’t matter today.”

Bitcoin, which was created in 2009, has become popular partly because of the 2008 financial crisis, which ended up destroying people’s faith in institutions like banks and governments, Novogratz said.

“In a lot of ways, it’s a parallel to the rise of Trump,” he said.

But even if there’s a bust, Novogratz said, he’s not shying away from investing in bitcoin.

“Bubbles happen around ideas that are right that actually changed the world,” he said.