To provide an infant drinking device with a more reliable aerator, the infant drinking device comprises a teat, a reservoir for holding a liquid, a connector for detachably connecting the reservoir to the teat, and an aerator. The aerator (e.g., a duckbill valve) includes a deformable opening (e.g., a slit) whereby internal/external pressure differential during use of the device is reduced in an open position of the opening by allowing air to enter through the opening into the reservoir and such that leakage of fluid from an inside of the drinking device to an outside of the drinking device is hindered in a closed position of the opening. During assembly of the teat, connector and reservoir, a minimally defined deformation of the opening of the aerator is enforced by at least one of a geometrical property and a material property of the teat or the connector.
