Shares of airline stocks are tumbling on Monday morning after billionaire investor Warren Buffett said Berkshire Hathaway (BRK-A, BRK-B) exited all of its airline stock holdings earlier this month. He made the comments during Berkshire’s annual shareholders’ meeting on Saturday.

American Airlines (AAL), Delta (DAL), and United Continental Holdings (UAL) all dropped more than 12% on Monday, while Southwest Airlines (LUV) fell more than 8%.

Berkshire picked up large positions in the airlines in late 2016, years after Buffett had sworn off buying an airline stock.

In a departure from his normal practices, Buffett went into detail about transactions he made in April, which would normally be disclosed in an SEC 13-F regulatory filing several weeks after the close of the second quarter. Specifically, he said in April that Berkshire sold $6 billion worth of securities from its massive stock portfolio.

“I wouldn’t normally talk about it, but I think it requires an explanation,” he said on Saturday. “We were not disappointed at all in the businesses that were being run and the management, but we did come to a different opinion on it.”

Because of the COVID-19 pandemic, airlines are among the industries being hurt by an exogenous shock “far beyond their control,” Buffett said. He later added that if Berkshire owned airlines now, “it would be a tough decision to decide whether to sustain billions of dollars in operating losses when you don’t know how long it’s going to happen or occur.”

Buffett also suggested that the pandemic might also change consumer behavior long-term, pointing out that he hasn’t cut his hair in seven weeks and has been wearing a sweatsuit instead of a suit.

“The world has changed for the airlines, and I don’t know how it’s changed, and I hope it corrects itself in a reasonably prompt way,” he said. “I don’t know whether the Americans will have now changed their habits or will change their habits because of an extended period if it happens that we’re semi shut down in the economy.”

Earlier, the “Oracle of Omaha” said the “future is much less clear” to him as to how business will turn out on the other side of the pandemic. What’s more, he said, if the airline business comes back at 70% or 80% there will still likely be “too many planes” and an “oversupply of airline seats.”

“[It] didn’t look that way when the orders were placed a few months ago when arrangements were made,” he said. “But the world changed for airlines and I wish them well.”

Julia La Roche is a Correspondent at Yahoo Finance. Follow her on Twitter.