Warren Buffett waves off Fitch's cut to America's credit rating - and says he's buying Treasuries as normal

• Warren Buffett isn't stressing about Fitch's cut to America's credit rating this week.
• Berkshire Hathaway continues to buy $10 billion of US Treasuries every Monday, he told CNBC.

Warren Buffett isn't stressing about Fitch's shock downgrade this week of the US credit rating from AAA to AA+.

"There are some things people shouldn't worry about," he told CNBC's Becky Quick. "This is one."

The famed investor and Berkshire Hathaway CEO noted that his conglomerate bought $10 billion of US Treasuries on Monday, the same amount it bought on Monday last week. He added that the only question is whether Berkshire will buy $10 billion of 3-month or 6-month Treasuries next Monday.

Berkshire ranks among the world's biggest corporate holders of US government debt. The company reported $104 billion of short-term investments in US Treasuries at the end of March.

Buffett recently underscored the increased value of the holding to Berkshire, as the Federal Reserve's hikes to interest rates have boosted bond yields. He estimated in April that Berkshire's Treasuries are yielding $5 billion or nearly a 5% return annually — and the Fed has hiked rates further since then.

Buffett told CNBC he doesn't agree with all of the federal government's actions, but he remains fully confident in Treasuries and the US dollar.

"The dollar is the reserve currency of the world, and everybody knows it," he said.

Fitch's rating cut spooked investors this week, as it signaled reduced confidence in the safety of US government debt. The credit-rating agency made the move because of the country's rising debt level, weakening governance, and an "expected fiscal deterioration over the next three years."

Buffett is known for his unwavering optimism when it comes to America's prospects. He's also dismissed concerns about de-dollarization and the US government defaulting on its debt in recent months.