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(CNN Business) —  

Warren Buffett is making an even bigger move into banks.

Last quarter, Berkshire Hathaway (BRKA) took a $4 billion stake in JPMorgan Chase (JPM), according to regulatory filings posted Wednesday.

Berkshire also grew its investment in Bank of America (BAC), Goldman Sachs (GS), BNY Mellon (BK) and US Bancorp (USB) though the company slightly lowered its stake in Wells Fargo (WFC).

Buffett has long had a good relationship with JPMorgan Chase CEO Jamie Dimon. He’s partnered with the chief executive, as well as Amazon CEO Jeff Bezos, on a new health care venture for employees, and has recommended Dimon’s annual investor letter as a must-read.

He said in an interview with Yahoo Finance earlier this year that he regretted not investing in JPMorgan Chase sooner.

“I should’ve [invested],” Buffett said. “Very obviously. I mean, it’s been a terrifically run operation. And it was very cheap, just like a number of others were.” He also said he personally owns shares of JPMorgan Chase.

Big banks have raked in strong profits this year, though their stocks have lagged behind the broader market. Analysts have blamed rising bond yields, global trade tensions and growing competition from non-bank lenders, though some say the sector is undervalued.

Buffett also raised his stake in Apple (AAPL), which is Berkshire’s largest stock holding, the filings show. The iPhone maker has been dragging down markets, and fell Wednesday for a fifth consecutive day.