Abstract : Numerical simulations of viscous flow problems with complex moving boundaries commonly require the solution of the fluid equations on unstructured and deformable dynamic meshes. In this paper, we present a time-accurate methodology for computing the unsteady diffusive fluxes arising from such problems, and highlight its impact on the accuracy of the overall flow simulation. We illustrate this methodology with a viscous flow problem related to a supersonic aeroelastic application. The numerical schemes presented in this paper can be directly extended to the computation of turbulent flows on moving grids.