The present invention relates to a hydraulic distributor (2) of a servo-control (1) of an aircraft, the hydraulic distributor comprising main distributor member (10) and emergency distributor member (20) that are coaxial, said emergency distributor member (20) being caused to move by said main distributor member (10) in the event of said main distributor member (10) seizing, said hydraulic distributor being provided with a detector device (60) for detecting said seizing. The detector device (60) is provided with a reed switch (66) and with amplification means (62, 69, 68) for amplifying said movement of the emergency distributor member, said amplification means comprising a lever (62) having a magnetized free end (62′) that activates said reed switch (66) in the event of said emergency distributor member (20) moving.