Treasuries are heading for their biggest back-to-back quarterly advance in more than four years. Economists say the gains won’t continue into 2017.

The Bloomberg U.S. Treasury Bond Index has returned 5.5 percent since the end of 2015, the most since the combined third and fourth quarters of 2011. The rally snowballed last week after the U.K. voted to leave the European Union, driving a rush for the safest assets.

JPMorgan Chase & Co., Standard Chartered Plc, TD Securities Ltd. and Standard Bank Group Ltd., the four firms that have updated their Treasury forecasts since the U.K. referendum, all see 10-year yields rising 12 months from now. Standard Bank is calling for the biggest increase, to 1.85 percent, versus 1.47 percent Wednesday.

“Treasury prices are too high,” said Enna Li, a debt investor in Taipei at Mirae Asset Global Investments Co., which oversees $83 billion worldwide. “I wouldn’t buy any. The U.S. economy is still fine.”

Treasuries were little changed as of 10:29 a.m. in London, according to Bloomberg Bond Trader data. The price of the 1.625 percent security due in May 2026 was 101 1/2. The yield on the world’s benchmark bond plunged 31 basis points in the two days after the Brexit vote.

U.S. gross domestic product expanded at a 1.1 percent annualized rate in the first quarter, compared with a previously estimated gain of 0.8 percent, a Commerce Department report showed Tuesday in Washington.

Mirae’s Li said the GDP data shows the world’s biggest economy is performing well versus its peers. Britain’s decision to leave the EU has raised concern the U.K. will fall into a recession. In Japan, an inflation gauge monitored by the central bank is stuck below zero.

Some analysts say it’s too soon to call the Treasuries rally over.

“The increasingly uncertain outlook for the global economy, and the Fed’s reluctance to tighten, and investors’ desire for yields remain key support factors,” said Nick Stamenkovic, a fixed-income strategist at broker RIA Capital Markets Ltd. in Edinburgh. “Treasuries may have taken a pause in the past few days, but I see renewed rise in risk aversion pushing 10-year yields toward 1.25 percent, if not lower.”

Federal Reserve Governor Jerome Powell said Tuesday global risks have shifted further to the downside after Britain’s vote to exit the European Union, introducing new uncertainties that may merit reassessing monetary policy.

The U.S. is scheduled to report personal income and spending levels as well as an inflation index monitored by the Fed, all on Wednesday.