A method for stabilizing a condensed phase composition in a process of manufacturing a polyester from cyclic ester monomer comprising the steps of devolatilizing a reaction mixture, which contains i) at least one polymerizable cyclic ester, ii) at least one catalyst and optionally at least one initiator, to produce a vapor stream and a molten residue, wherein the vapor stream includes mainly i) the at least one polymerizable cyclic ester and ii) the at least one catalyst and/or the at least one initiator and/or a reaction product or a residue of the at least one catalyst and/or the at least one initiator and condensing the vapor stream to form the condensed phase composition, wherein at least one polymerization inhibitor is added as stabilizer to the reaction mixture and/or to the condensed phase composition in an amount so that the degree of conversion of the polymerizable cyclic ester in the condensed phase composition is not more than 15%, wherein the degree of conversion is 100▪(c0−CF)/c0, wherein c0 is the initial concentration of the cyclic ester in the condensed phase composition obtained by the condensation of the vapor stream and CF is the concentration of the cyclic ester in the condensed phase composition after addition of 150 ppm of tin octoate as catalyst and of 100 mmol/kg of ethyl-hexanol as initiator to the condensed phase composition and a subsequent heat treatment of condensed phase composition under inert atmosphere conditions for 12 hours at 160° C.