The invention provides a stabilizer for an aqueous dispersion of an acrylic polymer that is obtained by successive copolymerization in random order of a monomer mixture A consisting of particular amounts of styrene or methyl styrene, acrylic acid or methacrylic acid, and optionally another comonomer, and a monomer mixture B consisting of particular amounts of styrene or methyl styrene, a (cyclo)alkyl methacrylate having 1-12 carbon atoms in the (cyclo)alkyl group, and optionally another comonomer, in the presence of a particular amount of a polybutadiene having a number average molecular weight of 1500-10000, the carboxylic acid groups from the (meth)acrylic groups being at least partly ionized. The invention also pertains to an aqueous dispersion of an acrylic polymer thus stabilized.