Berkshire Hathaway chairman Warren Buffett, who for decades avoided tech stocks, has steered his firm heavily into the industry with 43% of the firm’s portfolio now represented by Apple stock ($91 billion). This according to a recent article in MarketWatch.

While the heavy tech weighting runs counter to a diversified approach, the article notes that Buffett once described diversification as “protection against ignorance, “ and a strategy that “makes little sense if you know what you are doing.”

Earlier this year, Buffett explained, “I don’t think of Apple as a stock. I think of it as our third business,” adding, “It’s probably the best business I know in the world.”