We study the contributions of resonances to mixing. Both and hybrid states are considered. Assuming reasonable values for the resonance parameters, we find relatively sizeable individual contributions to both ΔmD and ΔΓD. We derive a variant of the GIM cancellation mechanism for the resonance amplitudes and show that broken SU(3) can allow for appreciable residual effects. Additional input from meson spectroscopy and lattice gauge simulations will be needed to improve the accuracy of these predictions.