Stabilized polyester molding compositions in which the stabilizer is a carbodiimide of the formula ##STR1## where R is hydrogen, alkyl, halogen or nitro, at least one of the substituents R in the ortho-position to the carbodiimide group must differ from hydrogen, and the carbodiimide molecule contains, as substituents R, 2 alkyl groups and 2 nitro groups, or from 4 to 6 chlorine atoms, or 2 alkyl groups and from 4 to 6 chlorine atoms, or 2 chlorine atoms and 2 nitro groups, or 4 chlorine atoms and 2 bromine atoms.