  We present preliminary results for the charm quark mass in the $N_f=4$ RGI
scheme. These were obtained using $N_f=2+1$ CLS ensembles with $\mathcal{O}(a)$
non-perturbatively improved Wilson fermions. We employed five different lattice
spacings, ranging down to $a\lesssim 0.04$ fm and realized approximately
physical pion and kaon masses, with ensembles spread out along three different
trajectories in the quark mass plane, enabling a thorough study of the
dependence on the lattice spacing and the light and strange sea quark masses.
We sketch our analysis strategy and find that the dominant errors at present
are due to the renormalization and scale setting uncertainties.
