Mass limits on CTCV J2056–3014 determined by rotation at the Kepler period (P_K) and the onset of pycnonuclear reactions (for carbon WD). A minimum mass (solid square) of 0.56 M_⊙ is obtained if CTCV J2056–3014’s rotational period of 29.6 s is close to the mass-shedding limit. The upper mass limit (solid triangle) of around 1.5 M_⊙ results from the onset of pycnonuclear reactions if CTCV is a carbon WD.