Intermediate-resolution optical spectra of the X-ray transient J0422+32, obtained during the 1993 December mini-outburst, show a strong modulation in radial velocities and equivalent widths of all the emission lines, with a period of 0.2127+/-0.0013d (5.1h). This modulation is in good agreement with the photometric period of 0.2121d reported during both this and the original outburst. In particular, the complex HeII lambda4686 emission profile displays an intense S-wave with a velocity semi-amplitude of ~755 km s^-1. We discuss the implications of this emission originating either in the hotspot or on the heated face of the companion star. In the first case a mass function f(M)~1.2M_solar is implied, whereas in the latter case f(M)~9.5M_solar.