Aqueous dispersions comprising a polyurethane composed of a) diisocyanates, b) diols of which b1) from 10 to 100 mol %, based on the total amount of diols (b), have a molecular weight of from 500 to 5000, and b2) from 0 to 90 mol %, based on the total amount of diols (b), have a molecular weight of from 60 to 500 g/mol, c) monomers other than the monomers (a) and (b), containing at least one isocyanate group or at least one isocyanate-reactive group and further carrying at least one hydrophilic group or potentially hydrophilic group by means of which the polyurethane is made dispersible in water, d) if desired, further, polyfunctional compounds other than the monomers (a) to (c), containing reactive groups which are alcoholic hydroxyl groups, primary or secondary amino groups or isocyanate groups, and e) if desired, monofunctional compounds which are other than the monomers (a) to (d) and contain a reactive group which is an alcoholic hydroxyl group, a primary or secondary amino group or an isocyanate group, obtainable by reacting the monomers a), b), c), and, where used, d) and e) in the presence of a cesium salt.