Lighting device for a motor vehicle

The device (1) has a casing (2) fixed to a motor vehicle via a mounting interface, and an optical module mounted on the casing via another mounting interface (25) and for emitting light beam. The casing has a deformation zone (70) placed near one of the interfaces. The zone is highly deformable than the interface to transfer thermal expansion from the interface to the zone. The casing has another deformation zone (71) with a thermal expansion coefficient higher than that of a material of an element of the corresponding interface adjacent to the former deformation zone.