The companion mass ratio distribution (CMRD) of main sequence binaries is a crucial physical quantity for understanding the evolution of stars in binary systems and for constraining models of binary star formation. However, although much work has been done during the last years, the shape of the CMRD remains rather uncertain. We present a population synthesis study of white dwarf-main sequence (WDMS) binaries in the Galactic disk aimed at constraining the properties of the CMRD. To this end, we computed a set of Monte Carlo simulations aimed at reproducing the WDMS binary population observed by the SDSS. We used different prescriptions for the CMRD and we took into account all the known observational biases. We show that our simulations reproduce reasonably well the observed distributions of masses and luminosities of the white dwarf star and of spectral type of the main sequence star. Moreover, our simulations place constraints, albeit weak, on the shape of the CMRD.

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