The invention relates to a tip-cap assembly (30) adapted to close the fluid passageway (14) of the distally projecting tip (13) of an injection system (10), said tip-cap assembly (30) comprising:- an elastomeric inner cap (50) having a distal face (53) and a radial rim (57), and a length L2 defined as the distance between the distal face (53) and the radial rim (57),- a rigid outer cap (40) which is or can be securely disposed around said elastomeric inner cap (50), said rigid outer cap comprising a shoulder (42f) and at least one abutment surface (42e), and a length L1 defined as the distance between the at least one abutment surface (42e) and the shoulder (42f),wherein the elastomeric inner cap (50) is distally blocked by the contact between the distal face (53) and the at least one abutment surface (42e) and proximally blocked by the contact between the radial rim (57) and the shoulder (42f),and wherein the length L1 is greater than the length L2 in order to allow a limited translation of the elastomeric inner cap (50) within the rigid outer cap (40).
