Abstract: A lock for an extension ladder of the type having a movable frame section and a stationary frame section includes a first member forming a guideway which has an open end for receiving stations of the ladder and a second member forming an arm for guiding the lock past the stations of the ladder when the ladder is being extended or retracted. The first member has an elongated projection extending downwardly at the open end of the guideway for containing the stations within the guideway. A pivotal connection between the first member and the second member is located to a first side of a center line of the lock and the projection is located to a second side of the center line when the lock is freely hanging. When the open end of the guideway is closed by the second member, the tip of the projection, a cam surface of the second member, and the pivotal connection are generally in the same plane which forms an angle of 90.degree. or less with the projection.