The invention relates to an assembly for closing a tube, said assembly comprising a tube head (3) that has a neck (10) and a closing cover (5) for closing said neck (10), the assembly further comprising a cap (30) which is provided with a piercing element (7) designed to perforate said closing cover (5), the neck (10) and cap (30) being configured such that the cap (30) is guided on the neck (10) into a closed position in which said piercing element (7) has perforated the closing cover, passing via an intermediate position in which the piercing element (7) has finished piercing said closing cover (5), and this also produces a material deformation which seals the closure, said assembly being configured such that the intermediate position is passed through prior to the material deformation which seals the closure.