An apparatus, method and computer program is described comprising: receiving a first measurement report from a first communication node of a mobile communication system, wherein the first measurement report includes downlink measurement data generated at a user device in response to a positioning reference signal sent by the first communication node; receiving a second measurement report from the first communication node, wherein the second measurement report includes uplink measurement data generated at the first communication node in response to an uplink reference signal sent by the user device; determining an integrity of the measurement data based on a comparison of said uplink and downlink measurement data; and setting an integrity verification notification in accordance with the determined integrity.