Longtime value investor Bill Nygren warned that the popular benchmark S & P 500 is not as diversified as it used to be, and he is picking cheap stocks outside the dominant tech sector. Nygren, portfolio manager at Oakmark Funds for 40 years, said the technology sector has grown so powerful in the S & P 500 that the 25 or so largest names make up about half the investment. “It’s not nearly as diversified as investors think it is. I think we will see investors revisit the idea of the S & P 500 being kind of the low-risk way to invest in equities,” Nygren said on CNBC’s “Squawk on the Street” on Monday. The large-cap benchmark has rallied about 20% to hit consecutive record highs, powered by a small handful of megacap tech names such as Nvidia and Meta Platforms. Many view this narrow breath as a sign of fragility in the bull market. Nygren said the negative bias toward value stocks pushed him to look for companies with inexpensive stocks that have sizable buyback programs in place, so that the share price would appreciate on its own without other investors following suit. “It’s become so important to us that we invest with companies that are taking matters into their own hands and using excess capital to repurchase their own stock,” Nygren said. He highlighted Corebridge Financial in his portfolio, which is a $15 billion retirement services and life insurance company that was spun off from AIG recently. Corebridge is trading around $28 per share, and Nygren sees the stock gaining a book value of $50 by the end of 2025, or four to five times earnings. The investor said the company could buy back 20% of their stock a year. “It’s a name not many people know about,” Nygren said. “They don’t have to depend on other investors to recognize the value. They just keep reducing the flow.” Correction: This article was updated to reflect that Bill Nygren appeared on “Squawk on the Street.” A previous version named an incorrect show.