Mounting of a sight on a firearm semi-automatic or automatic shotgun of the type comprising a housing through which a screw extends which receives a threaded securing cap which is notched to cooperate with an elastic stub at one end of the housing, said mounting being characterized in that it comprises a support having a ring at one end designed to engage with the screw and comprising, on the one hand, a hole designed to receive the elastic stub and, on the other hand, a second elastic stub designed to cooperate with the notches, said ring being connected by a tab with a small plate that is folded over to extend above the barrel, means being provided to secure the sight onto the small plate.