Hedge fund investor Bill Miller is making a $400 million bet on Bitcoin (BTC). The Miller Opportunity Trust filed with the U.S. Securities and Exchange Commission (SEC) on Friday, to invest in the Grayscale Bitcoin Trust —seeking indirect exposure to BTC. The filing will become effective 60 days after the filing date.

“The fund may seek investment exposure to bitcoin indirectly by investing in the Grayscale Bitcoin Trust, an entity that holds bitcoin.” Explained the SEC filing.

However, Miller’s fund will not be able to add any additional investment in the Grayscale Trust if its total Bitcoin exposure surpasses 15%. With the fund’s limited Bitcoin exposure, the Grayscale Bitcoin Trust outlay could surpass $300 million.

The Miller Opportunity Trust’s SEC filing further explains: “The fund will not make any additional investments in the Grayscale Bitcoin Trust if, as a result of the investment, its aggregate investment in Bitcoin exposure would be more than 15% of its assets at the time of investment.”

Grayscale reached the milestone of $30 billion in net cryptocurrency assets under management — $24 billion of it were in Bitcoin. Furthermore, the company provides eight more cryptocurrency investment tokens.

Bill Miller supported Bitcoin since day one

Miller was one of Bitcoin’s early supporters. The popular investor said in 2014 that he bought the currency as a personal investment. In 2017, CNBC reported that Miller has 30% of his MVP 1 fund in Bitcoin.

The Friday filing says that the price volatility is due to lack of usage of Bitcoin: “there is a relatively small use of Bitcoin in the retail and commercial marketplace in comparison to the relatively large use of Bitcoin by speculators,” Stated the Friday SEC filing.

Meanwhile, Bitcoin had blasted above the $43,000 on Monday — the cryptocurrency’s highest record to date. The price surge followed news that Tesla bought $1.5 billion worth of the cryptocurrency. Furthermore, the digital token’s market capitalization surpassed that of Facebook (NASDAQ: FB) and Tesla (NASDAQ: TSLA) following the price surge.