A base plate with an extension which defines a pair of notched seats is secured to the frame of a pivoting door in the gap between the frame and the door. A stop plate, made from a disk of stiff metal plate having an aperture of predetermined shape and with three bent sections that form a hand grip, is initially placed over the extension on the base plate while the door is closed. The stop plate aperture allows the stop plate to be displaced horizontally and downwardly until the section of stop plate defining the opposite end of the aperture lies within the upper notched seat and rests on the base plate. The stop plate confronts the face plane of the door; the door is prevented from opening beyond the door frame by the combination of the stop plate and the base plate.