Mr Buffett has said the US economy will be in a "shambles" during 2009
US financier Warren Buffett's holding company, Berkshire Hathaway, has lost its top credit rating.
Ratings agency Moody's cut the debt rating from Aaa, the highest, to Aa2, meaning that it thinks the company is less likely to pay back its debt.
Mr Buffett admitted last month he made some "dumb" mistakes in 2008, when Berkshire's profits fell 62% - the worst performance in its 44 years.
Berkshire's range of investments are seen as a bellwether of the US economy.
The move is all the more noteworthy, as Berkshire is a significant investor in Moody's.
The outlook on Berkshire's debt is stable, meaning Moody's does not expect to cut its rating again anytime soon.
In his annual letter to investors, Mr Buffett said his errors included buying stakes in two Irish banks and investing in oil company Conoco Philips when the crude price was at its peak.
He predicted that the US economy would be in a "shambles" throughout 2009 and beyond.
Berkshire's equity holdings include financial stocks such as Goldman Sachs, American Express Co and Wells Fargo & Co, which have all suffered big declines.
Mr Buffett, ranked as the world's second-richest man by Forbes magazine, also owns stakes in Coca-Cola, reinsurer Swiss Re and car insurer Geico.
Now, there are only four US companies with Moody's top Aaa debt rating - Exxon Mobil, Microsoft, Johnson & Johnson and Automatic Data Processing.
Class A shares in Berkshire have dropped by 7.9% this year, closing on Wednesday at $88,960 a share.