Oligo(β-amino ester)s, obtainable by aza-Michael addition of primary monoamines or primary or secondary diamines to diesters from monoethylenically unsaturated monocarboxylic acids and diols, is included in a surfactant-containing aqueous detergent solutions in order to prevent the transfer of textile dyes from colored textiles to uncolored textiles or textiles of other colors when washing textiles in the detergent solutions.