Closure cap intended to close off an open end of a reservoir, comprising a substantially cylindrical body (12) of longitudinal axis (Z) that is intended to be mounted on the open end of the reservoir and is provided with a flow orifice (12e) and a lid (14) that is articulated about a transverse pivot axis (A0) with respect to the body (12), by means of at least two hinges (16), between an open position of the flow orifice (12e) and a closed position of said flow orifice (12e), said lid (14) having an outside diameter greater than the outside diameter of the body (12) and forming a radial lip, said closure cap (10) also comprising a return member (18) that is disposed in a plane passing between the two hinges (16) and is able to keep the lid (14) in each of the positions. The return member (18) has a bent shape configured to be inserted into cavities (12f, 14d) made in the body (12) and in the lid (14), respectively, and to be flush with the radial lip of the lid (14) in the closed position.