(Bloomberg) -- Famed fund manager Bill Miller extended his endorsement of Bitcoin by reserving the right for one of his portfolios to indirectly invest in the largest cryptocurrency.

The Miller Opportunity Trust may invest in the Grayscale Bitcoin Trust, a vehicle institutions use for Bitcoin exposure, a filing with the U.S. Securities and Exchange Commission shows. Miller’s fund would be prohibited from additional investing in the Grayscale trust if its aggregate Bitcoin exposure tops 15%.

Read more: JPMorgan Says Flows to Grayscale Trust Key to Bitcoin’s Outlook

Miller was one of Bitcoin’s earliest proponents among major investors. He said in 2014 he owned the cryptocurrency personally, and in October 2017 told The Wall Street Journal that his MVP 1 fund had about 30% of its assets in Bitcoin.

The Friday filing pointed out that currently “there is relatively small use of Bitcoin in the retail and commercial marketplace in comparison to the relatively large use of Bitcoin by speculators,” leading to price volatility.

The $2.7 billion Miller Opportunity Trust has a five-year return that puts it among about the top 2% of peers, according to data compiled by Bloomberg. It was mostly invested in equities as of Dec. 31.

Bitcoin has pulled back since reaching a record of nearly $42,000 in early January. It’s almost quadrupled over the past year and was trading at about $39,100 as of 7:26 a.m. in London.

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