A window vent stop for use in a sliding sash window assembly or a sliding door assembly. The vent stop has a housing adapted to be disposed in a recess in the non-movable sash member. This housing includes a cavity with a bottom plate therein. The tumbler has at least one pivot for pivotally securing the tumbler to the housing for movement between an extended position, to prevent movement of the sliding member and a retracted position, to allow movement of the sliding member. Also within the housing is a spring for biasing the tumbler. The housing has one or more flexible members extending from the end walls of the housing that secure the housing to an opening in a window sash when a portion of the window sash is positioned between the underside of a lip on said housing and the flexible member.