A mixture for the treatment of urea-containing fertilizers comprises a) at least one (thio)phosphoric acid triamide of the general formula (I) R1R2N—P(X)(NH2)2 and/or (thio)phosphoric acid diamide of the general formula (II) R1O—P(X)(NH2)2, X denoting oxygen or sulfur, R1 and R2 independently from each other being hydrogen, substituted or unsubstituted 2-nitrophenyl, C1-10-alkyl, C3-10-cycloalkyl, C3-10-heterocycloalkyl, C6-10-aryl, C6-10-heteroaryl or diaminocarbonyl, where R1 and R2 together with the nitrogen atom connecting them can also form a 5 or 6-membered saturated or unsaturated heterocyclic group, which optionally may also comprise one or two additional heteroatoms selected from the group consisting of nitrogen, oxygen, and sulfur, as component A, and b) at least one compound comprising an amino group having a boiling point of more than 100° C. as component B.