A coating composition comprising a film forming binder of a. a modified polyepoxy resin comprising the reaction product of a polyepoxide resin, dimer fatty acids and an organic polyisocyanate, wherein the modified polyepoxide resin has a weight average molecular weight of 1000 to 50,000; and b. at least one amino functional silane crosslinking agent; wherein the coating composition preferably contains pigments and has excellent adhesion to aluminum and aluminum alloy substrates and provides excellent corrosion resistance and is particularly useful as a primer for such substrates.