  ${{\cal N}=4}$ supergravity is understood to contain a $U(1)$ anomaly which
manifests itself via the nonvanishing of loop-level scattering amplitudes that
violate a tree-level charge conservation rule. In this letter we provide
detailed evidence that at one loop such anomalous amplitudes can be set to zero
by the addition of a finite local counterterm. We show that the same
counterterm also cancels evanescent contributions which play an important role
in the analysis of ultraviolet divergences in dimensionally regularized
gravity. These cancellations call for a reanalysis of the four-loop ultraviolet
divergences previously found in this theory without the addition of such
counterterms.
