Michael Burry, the investor made famous by The Big Short movie, has taken out a major short position against Cathie Wood’s Ark Innovation exchange-traded fund (ETF).

According to second-quarter 13F filings from the United States Securities and Exchange Commission, Burry’s hedge fund, Scion Asset Management, has purchased $31 million worth of bearish put options against 235,000 shares of the ETF. Put options are a way of profiting from the decline in value of a stock or fund.

The Innovation ETF is the largest Ark fund with $22.62 billion in assets. It invests in a range of disruptive technology companies, including Tesla, Square, Coinbase, as well as the Grayscale Bitcoin Trust (GBTC).

Burry wasn’t the only firm to short Ark’s flagship fund, according to the filings. Laurion Capital Management held roughly $171 million worth of put options against 1.3 million shares, while GoldenTree Asset Management, Moore Capital Management and Cormorant Asset Management also held large bearish positions.

But Wood appeared to relish the challenge, tweeting on Monday:

“To his credit, Michael Burry made a great call based on fundamentals and recognized the calamity brewing in the housing/mortgage market. I do not believe that he understands the fundamentals that are creating explosive growth and investment opportunities in the innovation space.”

Wood is a firm believer in crypto, and in July, Ark partnered up with Switzerland-based 21Shares, with the goal of creating a Bitcoin (BTC) ETF.

In the same month, Ark Invest purchased more than 450,000 GBTC shares in two separate buys, and in April, Ark purchased $110 million of Coinbase shares, some of which were for the Innovation ETF.

Burry, however, is a crypto bear and has been warning about “unsustainable valuations” in the market for a few months. In June, he warned that retail investors could be lured into “the mother of all crashes” by investing in cryptocurrencies and meme stocks. He tweeted:

“All hype/speculation is doing is drawing in retail before the mother of all crashes. When crypto falls from trillions, or meme stocks fall from tens of billions, #MainStreet losses will approach the size of countries. History ain’t changed.”

Burry found fame when he called the housing market’s collapse during the global financial crisis and profited enormously from the subprime mortgage crisis. He was the main character in Michael Lewis’ book The Big Short that later turned into an Oscar-winning movie in which he was played by Christian Bale.