Oil-in-water emulsions which contain (i) 100 parts by weight of a polydimethylsiloxane (P) having aminoalkyl groups and having an amine number of at least 0.1 meq/g of polydimethylsiloxane (P), composed of units of the general formula I R.sup.1.sub.aR.sup.2.sub.bSiO.sub.(4-a-b/2), (I) in which R.sup.2 are aminoalkyl radials of the formula II --R.sup.3--NR.sup.4R.sup.5,, (II) (ii) protonating agent, (iii) water and (iv) not more than 5 parts by weight of emulsifier, are stable and provide for improved water repellency of porous and nonporous, absorptive and non-absorptive substrates treated therewith.