The invention relates to a composition based on an impact-resistant thermoplastic polyamide resin, comprising, as a blend—from 60 to 98 wt % of polyamide resin (A) and—from 2 to 40 wt % of a blend of at least one graft copolymer with polyamide blocks (B) composed of a polyolefin backbone and at least one polyamide graft in which the grafts are attached to the backbone by the residues of an unsaturated monomer (X) having a functional group capable of reacting with an amine-terminated polyamide, the residues of the unsaturated monomer (X) being attached to the backbone by grafting or copolymerization via its double bond, and of a non-reactive ethylenic polymer (C) that is miscible with (B) and has a density of below 0.960 g/cm3.