Abstract: The locking device may either be used with a conventional liftgate support or incorporated into the design of the liftgate support, to retain a hatchback-type door of a vehicle in an open position. The locking device of the present invention is for use with a liftgate support to retain a hatchback-type door in an open position even in cold weather or after the liftgate support has worn out. The liftgate support includes a housing cylinder and an elongated piston rod. The elongated piston rod is slidably positionable relative to the housing cylinder, one end of the elongated piston rod being received within the housing cylinder. The locking device is secured to the housing cylinder by two-sided tape proximate to where the elongated piston rod is received by the housing cylinder.