The wet fastness of direct dyes on cellulose substrates is improved by after-treatment with the reaction product of an amine with cyanamide, dicyanodiamide, guanidine or biguanidine which is further reacted with an N-methylol resin precursor, and heat curing in the presence of a catalyst. The unfixed portion of reactive dyes substantive to cellulose may also be given improved wet fastness by this treatment, so that washing to remove unfixed reactive dye may not be necessary.