The use of circular-section glass fibres in a mixture including at least one MXDZ polyamide, obtained from polycondensation of meta-xylylenediamine (MXD), with a C6 to C18 aliphatic (Z) dicarboxylic acid, and at least one aliphatic polyamide A obtained from the polycondensation of a unit selected from: a C6 to C12 lactam, a C6 to C12 amino acid, and an XY unit obtained from the polycondensation of a C4 to C18 aliphatic diamine (X), and a C6 to C18 aliphatic dicarboxylic acid (Y), circular-section glass fibres and optionally at least one impact modifier and/or at least one additive, said circular-section glass fibres and said mixture constituting a composition, said circular-section glass fibres being present from 30 to 75% by weight and with respect to the total weight of the composition, to improve the mechanical properties of said composition, including elongation at break, after processing, in particular by injection or compression moulding.