A network node (18) transmits, to a wireless device (12), assistance data (20) that indicates a search window (26) which is associated with a beamforming configuration. The search window (26) associated with the beamforming configuration may be a window within which a result (28) of a positioning measurement performed by the wireless device (12) on a positioning signal (20A) is expected to be for the associated beamforming configuration. The wireless device (12) may check whether a result (28) of the performed positioning measurement falls within the indicated search window (26), and deem the result (28) valid or invalid depending respectively on whether or not the result (28) falls within the indicated search window (26) according to that checking.