Watertight headlight comprising: - a shell to which an optic is fixed, said shell and said optic delimiting a watertight chamber, - an electric battery device and light sources powered by said battery device, said battery device and said light sources being installed in the watertight chamber, - a control element whose actuation controls the switching on of the light sources, which control element is installed in the watertight chamber, - the control element is actuated by a pushbutton installed in a formation produced in the optic, - and in which: the pushbutton has a proximal portion on which, in use, a user exerts an actuation pressure to control the switching on of the light sources, the rim of said proximal portion being provided with a watertight deformable flange ring, said flange ring being delimited by a lateral wall having an outer face and an inner face, said flange ring being provided, over the circumference of its distal rim, with a watertight seal, - the formation has a groove in which the watertight seal is fitted to form the watertight seal between the optic and the pushbutton, which formation has a lateral wall and a bottom wall, said groove being produced in said bottom wall, - a ring is installed in the formation so as to lock the watertight seal in position in the groove, which ring is installed around the flange ring and has an outer lateral wall, an inner lateral wall, a proximal transverse wall and a distal transverse wall, characterized in that: - the outer lateral wall of the ring has a diameter fitted to the diameter of the lateral wall of the formation and the inner lateral wall of said ring has a diameter fitted to the diameter of the outer lateral wall of the flange ring, - the distal transverse wall of the ring is secured to the bottom wall of the formation; or the outer lateral wall of said ring is secured to the lateral wall of said formation; or the outer lateral wall of said ring is threaded and is engaged in a complementary threading produced on the lateral wall of said formation. - a shell to which an optic is fixed, said shell and said optic delimiting a watertight chamber, - an electric battery device and light sources powered by said battery device, said battery device and said light sources being installed in the watertight chamber, - a control element whose actuation controls the switching on of the light sources, which control element is installed in the watertight chamber, - the control element is actuated by a pushbutton installed in a formation produced in the optic, - and in which: the pushbutton has a proximal portion on which, in use, a user exerts an actuation pressure to control the switching on of the light sources, the rim of said proximal portion being provided with a watertight deformable flange ring, said flange ring being delimited by a lateral wall having an outer face and an inner face, said flange ring being provided, over the circumference of its distal rim, with a watertight seal, - the formation has a groove in which the watertight seal is fitted to form the watertight seal between the optic and the pushbutton, which formation has a lateral wall and a bottom wall, said groove being produced in said bottom wall, - a ring is installed in the formation so as to lock the watertight seal in position in the groove, which ring is installed around the flange ring and has an outer lateral wall, an inner lateral wall, a proximal transverse wall and a distal transverse wall, - the outer lateral wall of the ring has a diameter fitted to the diameter of the lateral wall of the formation and the inner lateral wall of said ring has a diameter fitted to the diameter of the outer lateral wall of the flange ring, - the distal transverse wall of the ring is secured to the bottom wall of the formation; or the outer lateral wall of said ring is secured to the lateral wall of said formation; or the outer lateral wall of said ring is threaded and is engaged in a complementary threading produced on the lateral wall of said formation.