Federal Reserve Board Chair Janet Yellen raised fresh concerns about low inflation in a speech on Tuesday evening.

Minutes from the Fed’s November 1 meeting show that doubts exist among policymakers about whether low inflation is, in fact, transitory.

Wall Street is still counting on a December interest-rate hike, but future rate increases may be in doubt unless inflation and wages pick up.

Between Janet Yellen’s speech on Tuesday night and the minutes of the Federal Reserve’s November meeting, one message is becoming increasingly clear: Officials are becoming uncomfortable with their forecasts of a “transitory” period of inflation below the central bank’s target.

It means interest rates may not climb the way many on Wall Street expect.

As Yellen prepares to cede the helm of the central bank to her colleague Jerome Powell early next year, these concerns cast doubt over the Fed’s forecasts of several additional interest-rate increases in 2018 and 2019.

“I will say I am very uncertain about this,” Yellen said in remarks on Tuesday evening. “My colleagues and I are not certain that it is transitory, and we are monitoring inflation very closely.”

Traders think the Fed’s meeting on December 12 and 13 is too soon for a change of course, and markets have long priced in an additional interest-rate hike then. The Fed has raised interest rates four times in halting steps since December 2015, to a range of 1% to 1.25%, after having left them at essentially zero for seven years in response to the Great Recession.

Still, further hikes are far from certain. Minutes from the central bank’s latest policy meeting reaffirmed Yellen’s tone and suggested that others on the committee share her views:

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“Many participants observed, however, that continued low readings on inflation, which had occurred even as the labor market tightened, might reflect not only transitory factors, but also the influence of developments that could prove more persistent.”

Financial markets are on tenterhooks waiting for Powell, who has much less experience than Yellen in monetary policy and economics and has said little about interest rates, to speak on the record.

Yellen and her colleagues have previously expressed surprise at an inflation rate that has continued to undershoot the Fed’s official 2% target for much of the economic recovery – a trend that suggests the labor market is not fully healed despite a historically low 4.1% jobless rate.

Another sign of trouble: Wages are not rising for most Americans, leading to a loss of purchasing power despite low reported inflation readings.

Unless both wages and inflation begin to pick up soon, Fed officials under any leadership should reconsider their gusto to tighten financial conditions in a still fragile economy.