Long-time value investor Bill Nygren is warning that the popular benchmark S&P 500 is no longer as diversified as it once was and he's picking cheap stocks outside of the dominant technology sector. Nygren, a portfolio manager at Oakmark Funds for 40 years, said technology is so strong in the S&P 500 that about 25 of the largest companies account for about half of the investments. “It's not as diversified as investors think. I think we're going to see investors revisit the idea of the S&P 500 as a low-risk way to invest in stocks,” Nygren told CNBC's “Money Movers” on Monday. expressed in. The large-cap benchmark has risen about 20% to hit consecutive all-time highs, driven by a handful of big tech names such as Nvidia and Meta Platforms. Many consider this tight breathing to be a sign of bull market fragility. Nygren said the negative bias against value stocks leads him to look for companies with cheap stock prices and large buyback programs so the shares can appreciate on their own without being followed by other investors. “This has become so important to us that we invest in companies that are taking matters into their own hands and using excess capital to repurchase their own stock,” said Nygren, who focuses on that in his portfolio Corebridge Financial, a $15 billion retirement services and life insurance company, was recently spun off from AIG. Corebridge trades at about $28 a share, and Nygren expects the stock to have a book value of $50 by the end of 2025, or a multiple of four to five times earnings. The investor said the company can repurchase 20% of its shares every year. “Not many people know the name,” Nygren said. “They don't have to rely on other investors to recognize the value. They just keep reducing the flow.”