The present invention relates to a stabilizer composition containing at least one sterically hindered amine (HALS) in which the amino group carries a basicity-reducing substituent, at least one antioxidant containing one or more thioether groups and at least one liquid plasticizer containing carboxylate groups. The invention further relates to a polymer composition containing at least one sterically hindered amine (HALS) in which the amino group carries a basicity-reducing substituent, at least one antioxidant containing one or more thioether groups, at least one liquid plasticizer containing carboxylate groups and at least one silyl-terminated polymer, to the use of the stabilizer composition for stabilizing a silyl-terminated polymer or a sealant, adhesive, gasket, knifing filler or coating composition, especially a sealant, adhesive, gasket, knifing filler or coating composition containing a silyl-terminated polymer, against degradation by heat, light and/or oxygen, to the use of the polymer composition as or in a sealant, adhesive, liquid gasket, knifing filler or coating composition, and to a sealant composition or an adhesive composition, or a gasket composition, or a knifing filler composition or a coating composition comprising the polymer composition.