A method for manufacturing an optical-fibre sensor device is provided, including an enclosure defining a recess and an optical-fibre sensor including an optical-fibre and a device for holding the sensor that is rigidly connected to the optical fibre, the optical fibre passing through the holding device between two attachment points provided on the holding device. The method comprises the steps of: positioning the optical-fibre sensor in the enclosure to pass the fibre through two passage openings provided on the enclosure, the optical fibre generally extending along a longitudinal axis in the recess, which defines two optical-fibre portions in the enclosure, on either side of the holding device, each fibre portion extending between one of the points for attachment of the holding device and one of the passage openings in the enclosure, substantially in a straight line; holding the optical-fibre sensor in position; performing a differential elongation of the enclosure relative to the optical-fibre sensor in the longitudinal direction, and towards the outside of the enclosure, while the optical-fibre sensor remains held in position; attaching the optical fibre to the enclosure at the passage openings.