Crosslinkable aqueous polyurethane dispersions having a long shelf life containA) polyurethane which have carbonyl groups, are dispersed in water in the presence of ammonia or of organic amines and are obtainable by reactinga) organic polyisocyanates withb) compounds which contain one or more active hydrogen atoms and one or more salt groups or one or more groups capable of salt formation andc) carbonyl-containing mono- and/or polyalcohols andd) if desired chain extenders ande) if desired polyhydroxy compounds having molecular weights of from 500 to 8,000, andB) polyhydrazides.