A stabilizer composition containing (I) a compound of the formula (I) and (II) a compound of the formula (II) wherein the radicals R1 independently of one another are C1-C18 alkyl or C3-C12 cycloalkyl; the radicals X1 independently of one another are hydrogen, C1-C18 alkyl, C3-C12 cyclo-alkyl or a group of the formula (III-I); (III-I) the radicals X2 independently of one another are hydrogen, C1-C18 alkyl, C3-C12 cyclo-alkyl or a group of the formula (III-II); (III-II) and Y is C2-C12 alkylene.