JPMorgan CEO Jamie Dimon says bitcoin is worse than the most famous asset bubble in history.

The cryptocurrency is “worse than tulip bulbs,” Dimon said at a Barclays Conference on Tuesday, according to Bloomberg. That’s a reference to the arrival and boom of the tulip plant in 17th-century Europe. Its market boomed as people speculated on its price, and it all ended in panic selling.

He added that “it’s a fraud” that would eventually blow up.

Bitcoin has rocketed more than 350% this year while exploding in popularity, particularly in Asia. This rally “won’t end well,” Dimon said.

Most fund managers surveyed by Bank of America Merrill Lynch in September said that betting on its continued rise was the “most crowded” trade. Dimon said he would fire any trader that transacted bitcoin for being stupid.

Dimon isn’t alone in being skeptical of bitcoin. Robert Shiller, the Nobel-winning author who predicted the housing and tech bubbles, recently doubled down on his view that bitcoin is a bubble, telling Quartz it was the “best example right now” of one.