Process for the preparation of a composition comprising aliphatic polyester by ring-opening polymerization of cyclic ester monomers, said process comprising the steps of: (a) providing cyclic ester monomers and polymerization catalyst to a reactor, (b) melt polymerizing said cyclic ester monomers to form a composition comprising aliphatic polyester, (c) stabilizing the composition against aliphatic polyester depolymerization by incorporating therein or applying thereto at least one stabilizing agent thereby obtaining a melt-stable composition, and (d) optionally removing at least a portion of the residual cyclic ester monomers; wherein said stabilizing agent is a compound of formula wherein R 1 is hydrogen or C 1-6 alkyl; R 2 is selected from the group comprising hydrogen, C 1-6 alkyl, HO-C(=O)-CH(NHR 7)-(CH 2) n -C(=O)-, and C 1-6 alkylcarbonyl; R 3 is selected from the group comprising hydroxyl, C 1-6 alkoxy and -NH-(CH 2) p -C(=O)-OH; m is an integer selected from 0, 1 or 2; n is an integer selected from 1 or 2; p is an integer selected from 1 or 2; each R 4 is independently selected from hydrogen or C 1-6 alkyl; each R 5 is independently selected from hydrogen or C 1-6 alkyl; R 6 is selected from hydrogen, or a group of formula wherein * indicates the point of attachment to the S of formula, and R 7 is selected from the group comprising hydrogen, C 1-6 alkyl, and C 1-6 alkylcarbonyl; wherein compound of formula is present in an amount of at least 0.010 % by weight based on the total weight of said aliphatic polyester composition. (a) providing cyclic ester monomers and polymerization catalyst to a reactor, (b) melt polymerizing said cyclic ester monomers to form a composition comprising aliphatic polyester, (c) stabilizing the composition against aliphatic polyester depolymerization by incorporating therein or applying thereto at least one stabilizing agent thereby obtaining a melt-stable composition, and (d) optionally removing at least a portion of the residual cyclic ester monomers; wherein said stabilizing agent is a compound of formula wherein R 1 is hydrogen or C 1-6 alkyl; R 2 is selected from the group comprising hydrogen, C 1-6 alkyl, HO-C(=O)-CH(NHR 7)-(CH 2) n -C(=O)-, and C 1-6 alkylcarbonyl; R 3 is selected from the group comprising hydroxyl, C 1-6 alkoxy and -NH-(CH 2) p -C(=O)-OH; m is an integer selected from 0, 1 or 2; n is an integer selected from 1 or 2; p is an integer selected from 1 or 2; each R 4 is independently selected from hydrogen or C 1-6 alkyl; each R 5 is independently selected from hydrogen or C 1-6 alkyl; R 6 is selected from hydrogen, or a group of formula wherein * indicates the point of attachment to the S of formula, and R 7 is selected from the group comprising hydrogen, C 1-6 alkyl, and C 1-6 alkylcarbonyl; wherein compound of formula is present in an amount of at least 0.010 % by weight based on the total weight of said aliphatic polyester composition. R 1 is hydrogen or C 1-6 alkyl; R 2 is selected from the group comprising hydrogen, C 1-6 alkyl, HO-C(=O)-CH(NHR 7)-(CH 2) n -C(=O)-, and C 1-6 alkylcarbonyl; R 3 is selected from the group comprising hydroxyl, C 1-6 alkoxy and -NH-(CH 2) p -C(=O)-OH; m is an integer selected from 0, 1 or 2; n is an integer selected from 1 or 2; p is an integer selected from 1 or 2; each R 4 is independently selected from hydrogen or C 1-6 alkyl; each R 5 is independently selected from hydrogen or C 1-6 alkyl; R 6 is selected from hydrogen, or a group of formula wherein * indicates the point of attachment to the S of formula, and R 7 is selected from the group comprising hydrogen, C 1-6 alkyl, and C 1-6 alkylcarbonyl; wherein compound of formula is present in an amount of at least 0.010 % by weight based on the total weight of said aliphatic polyester composition.