Abstract: A locking device is provided for securing a protective bedliner to the interior of a pick-up truck cargo bed wherein the cargo bed has side walls with inwardly extending horizontal flanges and vertically, downwardly extending flanges spaced from the side walls of the truck. The side walls of the bedliner are provided with a plurality of circular apertures overlapping the bottom edges of the vertical flanges and a locking device is associated with each aperture. Each locking device includes a base plate engageable with the wall of the bedliner around an aperture and a flat planar locking tongue extending perpendicular to the base plate through the aperture. The locking tongue includes a shank portion having first and second substantially parallel edges disposed substantially perpendicular to the base plate and a retainer portion extending laterally from the shank portion substantially parallel to the base plate.