Investor Warren Buffett says he has been adding to his sizable stake in IBM during the third quarter as shares in the tech company slide, and that his Berkshire Hathaway has been spending about $500 million a week acquiring stock during recent market volatility.

Buffett appeared on CNBC Tuesday before dining with the winners of this year’s auction of a private lunch. Beijing’s Dalian Zeus Entertainment Co. paid $2,345,678.

“We bought [IBM] in the first quarter, and normally I wouldn’t tell you this, but we bought some in the third quarter,” Buffett told CNBC, according to Reuters.

The wire service noted that Buffett’s Berkshire Hathaway held 8 percent of IBM’s stock as of June 30.

IBM (NYSE: IBM) shares are down more than 10 percent in the third quarter but were trading up slightly Tuesday afternoon. IBM is down 23 percent over the past year.

Buffett said he bases his investments on a company’s prospects over the next five or 10 years, and he encouraged investors to take a long-term view.

“We’re buying because we like what we’re buying in relation to its long-term prospects,” he said.

Berkshire Hathaway recently disclosed a $4.5 billion investment in Phillips 66 even with energy companies being pummeled by low crude prices.

Buffett says he bases his investments on a company’s prospects over the next five or ten years.

Buffett also said Berkshire’s $32 billion agreement to buy Precision Castparts hasn’t slowed his other buying since it was announced last month.