Funding costs in China’s offshore market rose by the most in six years amid speculation that authorities in Beijing are making it more expensive to bet against the currency.

One-month offshore yuan swap points — a measure of the costs to borrow the yuan — jumped 1.73 basis points, the most since 2017 as the yuan gained Monday. As a result, the one-month implied yield surged to 5.5% from 2.7% on Friday, according to data compiled by Bloomberg.

Chinese policymakers have stepped up defense of the yuan in recent days as the currency weakened in the offshore market toward record lows amid contagion concerns on the potential default of one of China’s largest property developers and while one of the nation’s biggest shadow banks skipped payments on some of its investment products.

The People’s Bank of China has consistently set the fixing much stronger than analysts anticipated to slow the yuan’s decline. In addition, the funding costs of the offshore yuan, known as CNH, have steadily increased over the recent days, as Chinese banks refrained from adding yuan supplies in the swap market, according to traders. Liquidity demand also rose ahead of PBOC’s bill sales on Tuesday.

The currency climbed 0.2% Monday in offshore trading.

“The PBOC is squeezing the CNH funding,” said Bob Savage, head of markets strategy and insights at BNY Mellon Capital Markets. “The big China banks drained the CNH liquidity, i.e., didn’t add. They want foreigners short CNH to suffer a bit.”

(Corrects scope of move in headline.)