A window vent stop for use in a sliding member of 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 of the assembly. This housing includes a cavity with a bottom plate. A 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 toward the extended position. The housing has one or more flexible members extending from the end walls of the housing that secure the housing to the non-movable sash member.