Circle stock surged 10% on Friday. Tether was downgraded by S&P Global on Wednesday, reigniting questions about whether the world’s largest stablecoin can maintain its peg to the U.S. dollar.

S&P said in a note that it was cutting its rating of Tether to weak from constrained, citing increased exposure to higher-risk assets in the reserves to back its stablecoin USDT.

Stablecoins are cryptocurrencies that are pegged to another asset—in this case, the dollar. USDT had a total market capitalization of just under $185 billion on Thursday, according to the crypto data provider CoinMarketCap.

The ratings agency noted that corporate bonds, precious metals, Bitcoin, secured loans, and other riskier investments made up 24% of Tether’s reserves as of Sept. 30, up from 17% a year ago. That raises the chances of USDT becoming undercollaterized—whereby the assets would be worth less than the tokens in circulation.

“We wear your loathing with pride,” Tether CEO Paolo Ardoino said in a post on X addressed to S&P, adding that the company “is and remains extremely profitable.”

If the questions about Tether’s reserves linger, that could be good news for Circle Internet Group and its rival stablecoin USD Coin. Circle shares climbed 3.6% on Wednesday, and were up another 1% in after-hours trading.