  In our paper [SIAM J.\ Appl.~Math.\ 79-6 (2019),
https://doi.org/10.1137/19M1269403] we considered full waveform inversion (FWI)
in the viscoelastic regime. FWI entails the nonlinear inverse problem of
recovering parameter functions of the viscoelastic wave equation from partial
measurements of reflected wave fields. We have obtained explicit analytic
expressions for the first and second order Fr\'echet derivatives and their
adjoints (adjoint wave equations) of the underlying parameter-to-solution map.
In the present manuscript we correct an error which occurred in a basic result
and thus affected several other statements, which we have also corrected.
