Abstract: A portable auxiliary locking device for use with a door hung in a door jamb having a latch hole for receiving a horizontally extendible latch bolt. The locking device includes a plate thin enough to fit in the gap between the door and the doorjamb and long enough to extend inside the door and the doorjamb when the door is closed. The plate has at least one vertical slot and a tongue extending transversely from one end of the plate dimensioned to fit within the latch hole. A cross plate slides into a slot in the plate until a notch on the bottom edge of the cross plate engages the plate and locks the position of the cross plate. The cross plate includes an off-centered threaded aperture to accept a bolt. The bolt is adapted to be threaded through the aperture until it makes firm contact with the door or doorjamb.