Described is an aqueous one-component coating composition comprising dispersed polyurethane and phyllosilicate. The polyurethane carries acid groups which are at least partially neutralized with a hydrophilic base selected from inorganic bases and organic mono-amines. The hydrophilic base has a water solubility at 20° C. of at least 150 g/l, preferably of at least 200 g/l. The composition can be used for providing oxygen barrier properties to a polymer film.