The refractive index of freezing brine is important in order to, for example, estimate oceanic scattering as sea ice develops. Previously, no simple continuous expression was available for estimating the refractive index of brine at subzero temperatures. I show that extrapolation of the empirical formula for the refractive index of seawater by Quan and Fry [Appl. Opt.34, 3477 (1995)APOPAI0003-693510.1364/AO.34.003477] provides a good fit to the refractive index of freezing brine for temperatures above -24 degrees C and salinities below 180 per thousand.