An electrical connector assembly comprising a connector, a header with which the connector mates and a connector position assurance device wherein the connector comprises a latch arm having an engagement surface and a connector position assurance device receiving opening extending between the latch arm and a housing body of the connector, wherein the header has a complementary latching protrusion which is positioned to engage the latch arm as the connector and the header are moved from an unmated to a mated position, wherein the connector position assurance device comprises: a base portion having a top surface, a bottom surface, a base front end and a base back end, a latch engagement protrusion extending from the top surface; wherein in the fully inserted position of the connector position assurance device within the connector, the latch engagement protrusion is positioned beneath the latch arm 22, thereby preventing the latch arm from being moved downward; a beam extending from the front end of the base portion in a direction away from the back end of the base portion, the beam having a top side, a bottom side, a beam front end and a beam back end, the beam back end being attached to or integral with the base front end, the beam having an opening which extends through a portion of the beam to form a resiliently deformable top leg and a resiliently deformable bottom leg, a mating connector engagement protrusion extending from the resiliently deformable top leg provided proximate the top side of the beam, the mating connector engagement protrusion extending in a direction away from the bottom side; wherein the connector position assurance device is maintained in an initial position on the connector until the header cooperates with the mating connector engagement protrusion to force the mating connector engagement protrusion and the resiliently deformable top leg toward the bottom side of the beam, characterised in that the connector position assurance device, includes first and second top side notches (1020, 1021) provided along the top side of the beam proximate the mating connector engagement protrusion, and the first top side notch has side walls which are essentially perpendicular to a bottom wall of the first top side notch, wherein the side walls act as a stop surface to prevent the connector position assurance device from being moved by the cooperation of the first notch with a projection of the connector until the mating connector engagement protrusion and the resiliently deformable top leg are moved toward the bottom side of the beam. a base portion having a top surface, a bottom surface, a base front end and a base back end, a latch engagement protrusion extending from the top surface; wherein in the fully inserted position of the connector position assurance device within the connector, the latch engagement protrusion is positioned beneath the latch arm 22, thereby preventing the latch arm from being moved downward; a beam extending from the front end of the base portion in a direction away from the back end of the base portion, the beam having a top side, a bottom side, a beam front end and a beam back end, the beam back end being attached to or integral with the base front end, the beam having an opening which extends through a portion of the beam to form a resiliently deformable top leg and a resiliently deformable bottom leg, a mating connector engagement protrusion extending from the resiliently deformable top leg provided proximate the top side of the beam, the mating connector engagement protrusion extending in a direction away from the bottom side; wherein the connector position assurance device is maintained in an initial position on the connector until the header cooperates with the mating connector engagement protrusion to force the mating connector engagement protrusion and the resiliently deformable top leg toward the bottom side of the beam,