The present application relates to a breast pump system. The breast pump system comprises a vacuum path for creating a pressure reduction on a breast. A pump unit generates and releases a pressure reduction in the vacuum path, and comprises a vacuum pump (20). A leakage aperture (60) is configured to allow a controlled release of a pressure reduction in at least part of the vacuum path so that the pressure reduction in at least part of the vacuum path is released in the event that the pump unit fails to release the pressure reduction in the vacuum path. The vacuum pump (20) has a discharge port (22) for discharging air drawn from the vacuum path, and the leakage aperture (60) is disposed proximate to the discharge port (22) so that airflow discharged from the discharge port (22) is directed over the leakage aperture (60).