Former Federal Reserve Chairman Alan Greenspan is warning that sharply cutting taxes right now would be an economic “mistake.”

In an interview with Maria Bartiromo on the Fox Business Network Thursday, the 91-year-old Greenspan said it’s more important for President Trump and Congress to put the nation on a sustainable fiscal path by addressing rising entitlement spending driven by the aging of the U.S. population.

“Frankly, I think what we ought to be concerned about is the fact the federal debt is rising at a very rapid pace, and there’s nothing in this bill that will essentially stop that from happening," Greenspan said. "So my view is that we’re premature on fiscal stimulus, whether it’s tax cuts or expenditure increases. We’ve got to get the debt stabilized before we can even think in those terms.”