The present invention relates to a composition comprising (i) a crosslinkable polyolefin with hydrolysable silane groups (A), and (ii) a silanol condensation catalyst comprising an organic sulphonic acid (B) which comprises the structural element Ar-R 1 (I) wherein Ar is an aromatic group, which may e.g. be a benzene, naphthalene, phenantrene or anthracene group, and R 1 is an organic residue comprising at least 21 C-atoms, the organic sulphonic acid (B) further comprising one, two or more sulphonic acid groups, to an article, in particular a wire or cable, comprising such a composition, and to the use of such a composition for the production of an article.