Abstract: A window frame has one or more latches provided internally of a vent sill for pivotal engagement with a latch strike in the interior of a frame sill and a latch actuator extending outwardly through an opening in the inside face of the vent sill. A spring urges the latch into engagement with the strike with the latch and the actuator being movable in a linear horizontal direction so that a slot in the side of the actuator engages the edges of the opening through which the actuator extends to hold the actuator and the associated latch in a locked or non-pivotable condition. A second embodiment employs a similar pivotal and slidable latch member in a side frame of a horizontally movable vent frame which is pivoted into latching position inside an opening in a fixed vertical meeting rail and is retained in locked or non-pivotable condition by subsequent linear vertical movement of the latch to a restricted slot portion from which it cannot pivot from the locking position.