Abstract: Side and end boards are assembled to define a rectangular frame for a waterbed. External vertical grooves are formed on the exterior portions of the boards adjacent each of the corners. A metal bracing member comprised of two panels at a right angle to each other with 90.degree. turned in end flanges and a triangular web connecting the top edges of the panels and lying in a plane perpendicular to both panels is positioned above a corner of the frame. The flanges are fitted in the upper ends of the grooves and the bracing member then slid down over the corner so that the panels exteriorally straddle the corner. Each corner of the frame is treated in the same manner to provide an extremely simple assembly operation and resulting strong waterbed frame.