The fund noted it would not expose more than 15% of its $2.25 billion in assets to bitcoin.
"Not owning any bitcoin has been a massive mistake, and we expect that will continue to be true," the famed value investor's son wrote to clients.
"That's the opposite of what happens with most stocks," the mutual fund legend added.
Following bitcoin purchases by MicroStrategy and Square, Miller said every major investment bank and high net worth firm will eventually have exposure to bitcoin or commodities like gold.
Investor Bill Miller said last week that his MVP1 hedge fund has half of its investments in bitcoin.