A lockout device for selectively blocking linear movement of a movable frame member relative to a fixed frame member includes a lock tab pivotably mountable to the fixed frame member and having a contact surface configured to slidably engage a slide surface of the movable frame member when the lock tab has a first orientation, the movable frame member including a stop surface at one end of the slide surface, a holder for releasably holding the lock tab in a second orientation with the contact surface spaced from the slide surface, and a body mountable to the movable frame member and configured such that movement of the movable frame member in a first direction causes the body pivot the lock tab into the second orientation and movement of the movable member in a second direction causes the body to pivot the lock tab into the first orientation.