Abstract: This invention relates to a spring clip for biasing window sills up against the lower edge of a window sash either before or after the drywall has been installed, such clip being characterized by a horizontally-disposed leg fastenable to the underside of the sill, a spring finger depending from the front edge of the horizontal leg and extending rearwardly therefrom in acute angular relation, an upturned foot on the rear end of the spring finger, and means for fastening the sill and clip to the rearwardly-facing interior wall surface so as to hold the rear edge of the sill down in opposition to the bias exerted thereon by the clip. In versions of the clip designed for use with precast ceramic sills, a vertically-disposed integral leg depends from the rear end of the horizontal leg and fastening means, both integral and independent, are used to attach the vertical leg to the frame member in front thereof so as to leave a space for insertion of the drywall panel between it and the face-flange of the sill.