Billionaire investor Warren Buffett isn’t joining in on the bitcoin craze.

“I can say almost with certainty that they will come to a bad ending,” the CEO of Berkshire Hathaway Inc. said of cryptocurrencies in an interview with CNBC on Wednesday, Jan. 10.

“If I could buy a five-year put on every one of the cryptocurrencies I would be glad to do it,” Buffett said. “But I would never short a dime’s worth.”

Buffett clarified that he’s not interested in getting into the futures market for bitcoin, which launched on Cboe Global Markets and CME Group Inc. last month.

“I get in enough trouble with things I know something about,” Buffett said. “Why in the world should I take a long or short position on something I don’t know anything about?”

Buffett previously called bitcoin a “mirage” in 2014. He’s joined in his skepticism by JPMorgan Chase & Co. (JPM – Get Report) CEO Jamie Dimon, who called bitcoin a “fraud” in October. While Dimon scaled back his criticism some he still remains uninterested in piling in on the cryptocurrency.

Buffett’s second-in-command at Berkshire, Charlie Munger, agreed with Buffett, too. In the same CNBC interview, Munger said bitcoin and other cryptocurrencies were, in fact, bubbles.