The aqueous-based cross-linkable binder composition comprising (A) an aqueous dispersion of an aldehyde-functional polyurethane having a number average molecular weight of more than 1,000 and an average aldehyde functionality of ≧2, which polyurethane comprises ionic and/or non-ionic dispersing groups, and (B) a low-molecular weight aldehyde-reactive cross-linker selected from the group of low-molecular weight polyamines and low-molecular weight compounds comprising at least one group of one of the formulae E1—CHR1—E2 and H—C—(E1E2E3), wherein —E1, —E2 and —E3 are independently chosen from electron-withdrawing groups such as —P(═O)—O—, —CO—, —CN, —SO2—, —NO2 and wherein R1 has the meaning of hydrogen or a hydrocarbon radical having 1 to 10 carbon atoms. Preference is given to a coating composition wherein the ionic dispersing group is an anionic dispersing group selected from the group of carboxylate, sulphonate and/or phosph(on)ate salt groups, and/or wherein for the nonionic dispersing group use is made of a C1-C4 alkoxy poly C2-C3 alkylene-oxide group in an amount between 2.5 and 20 wt. %, based on the polyurethane.