Billionaire investor Warren Buffett said his investment in Tesco Plc was a “huge mistake,” as the U.K. supermarket leader’s share price remains close to an 11-year low amid declining sales and an accounting probe.

“I made a mistake on that one,” Buffett, 84, said in an interview with CNBC. “That was a huge mistake by me.”

Buffett’s Berkshire Hathaway Inc. has held Tesco shares since March 2006, when it acquired a stake for $328.7 million. By 2012, the holding had reached 5.08 percent of the grocer’s shares, worth about 1.3 billion pounds ($2.1 billion) . More recently, Buffett has been cutting the stake, owning 3.7 percent of the shares as of Dec. 31, according to Berkshire Hathaway’s annual report.

The holding’s value has slumped in the past year as Tesco has lowered its profit outlook amid a shift by shoppers toward discount and upscale chains. The shares are down 49 percent in the past 12 months, slumping 17 percent last week after new Chief Executive Officer Dave Lewis started a probe of accounting practices and suspended four executives after finding that Tesco overstated first-half profit estimates.

The stock was up 0.6 percent at 181.25 pence as of 3:02 p.m. in London, after closing Wednesday at the lowest price since April 2003.

Berkshire Hathaway remains Tesco’s fourth-biggest shareholder, based on the investor’s most recent filing.