Democratic Senator Elizabeth Warren backed recent comments on bitcoin by Treasury Secretary Janet Yellen during an interview with CNBC’s Squawk Box on Tuesday.

Asked if she agreed with comments saying the cryptocurrency was a “speculative” asset made by Treasury Secretary Janet Yellen late in February, the Senator said, somewhat coyly: “I think Janet’s a really smart woman.”

When pressed, she said, “‘Speculative in nature and going to end badly’ – I don’t think Janet left a lot of room for ambiguity.”

CNBC’s host also clarified that Yellen had actually said bitcoin could “end badly for some.”

The topic of bitcoin was brought up as a potential potential problem for a new “wealth tax” – proposed by Warren and Senator Bernie Sanders on Monday – that would see rich individuals charged 2% annually on their net worth above $50 million and 3% above $1 billion.

Yellen has been an outspoken critic of cryptocurrencies, calling them a “growing problem” and citing their use in illegal activity such as the drugs trade and terrorist funding. However, she’s also said that cryptocurrencies have the potential to “improve the efficiency of the financial system.”

See also: Bitcoin’s Rise Should Make Regulators Ask if the Fed’s Policies Have a Hand in It: WaPo