Apple’s stock, now sitting at its lowest level in four months, has faced a series of challenges this year. And it may have another one if Berkshire Hathaway really starts selling.

Warren Buffett’s holding company, Berkshire, has been one of Apple’s biggest backers. It owns a 5.9% stake, ranking behind only Vanguard Group, which holds 33% through its many mutual funds and exchange-traded funds, according to FactSet.

Berkshire’s most recent 13-F filing disclosing its holdings to the Securities and Exchange Commission showed it sold 10 million shares of Apple, or 1% of its stake, in the final three months of 2023. The conglomerate bought energy stocks including Chevron and Occidental Petroleum, the filing showed.

Based on Apple’s current share price, which had fallen for five consecutive trading sessions, including Tuesday morning, Berkshire’s stake in Apple is now worth $159 billion. It was valued at $167 billion in mid-February.

Apple stock, which still makes up about half of Berkshire’s equity portfolio, has come under pressure on a variety of fronts. The company has yet to offer detailed plans on an artificial-intelligence strategy and fewer iPhones are being sold in China, hurting overall revenue growth. A European Commission fine of nearly $2 billion over what it calls “abusive App Store rules,” disclosed Monday, isn’t good news either. Apple plans to appeal.

Apple’s stock has fallen 9% this year, while other members of the so-called Magnificent Seven—names such as Nvidia, Meta Platforms, and Amazon.com —are up by double-digit percentages. The broader market, as measured by the S&P 500, has climbed 7.6%.

The next problem for the stock could be if Buffett sells more Apple. “I could see him selling sooner or later,” Mizuho analyst Daniel O’Regan wrote in a Tuesday research note. “In fact, I would not be surprised if he is selling right now.”

The next 13-F from Berkshire, showing its holdings as of the end of the first quarter, is due around May 15.

O’Regan’s rationale is that Buffett is already “up a ton on his stake” and that the holding “feels in trouble” right now. The likely result of Berkshire sells more would be retail investors rushing for the exit and Apple shares getting “slaughtered,” the analyst said.

Berkshire didn’t respond to a request for comment.