A process for postcrosslinking a water-absorbing polymer comprises said polymer being treated with a postcrosslinker and, during or after said treating, being postcrosslinked and dried by temperature elevation, said postcrosslinker being a compound of the formula I where R1, R2, R3, R4, R5, R6, R7, R8 and R9 are each independently hydrogen, C1-C12-alkyl, C2-C12-alkenyl or C6-C12-aryl, wherein C1-C12-alkyl, C2-C12-alkenyl or C6-C12-aryl may be halogen substituted. The liquid-absorbing polymers are useful in hygiene articles and packaging materials.