Closure system for a container including a cap and a ring adapted to engage by screwing in order to seal the opening, the cap including an upper wall from which in a downwards direction there extends an annular skirt that has a lower annular end and a radially inner surface fitted with a thread. The ring has an annular top rim, an annular collar and a thread complementary to the thread of the cap provided between the collar and the rim of the ring. The skirt of the cap includes a projecting annular member forming a barrier and adapted to be supported against the whole periphery of the collar of the ring in a substantially radial direction.