  The charm-quark mass is typically not so far from the cutoff 1/a in lattice
simulations. Its determinant may then potentially introduce large cutoff
effects. We choose the O(a)-improved Wilson formulation and compute the vacuum
polarization effects in two rather different observables at one-loop order. One
is the quark-antiquark static force and the other the Schroedinger functional
coupling; in addition we investigate two more quantities resulting from the
latter. In all the cases the lattice artifacts due to the charm-quark are small
when compared to the gluonic effects. This indicates that the inclusion of
charm-quarks in dynamical fermion simulations is typically not a problem.
