Abstract: The invention pertains to a coating composition comprising a polyacetoacetate and a crosslinker for said polyacetoacetate wherein the crosslinker is present in an amount insufficient to crosslink all acetoacetate groups and the polyacetoacetate has a number average molecular weight less than 1000. The coating composition may also comprise an organosilane. The organosilane preferably comprises at least one amino group, amino-containing group, epoxy group, epoxy-containing group, mercapto group, mercapto-containing group, vinyl group, vinyl-containing group, isocyanate group, isocyanate-containing group, ureido group, ureido-containing group, imidazole group or imidazole-containing group. The coating composition is particularly useful as a primer for an aluminium substrate.