Composition for stabilizing iron compounds in an aqueous environment, which comprises a polycarboxylic acid or its salt (s), at least one monomeric or polymeric phosphonate comprising at least one phosphonic acid group, or its salt (s), at least one corrosion inhibitor comprising amino groups, and 1 -15 weight-%of polycitric acid or a copolymer of citric acid with polyols or glycerol, calculated as active ingredient from the total weight of the constituents in the composition, as dry.