Abstract: In a method for producing a homopolyester or copolyester obtainable from at least one cyclic monomer, the at least one cyclic monomer is polymerized in the presence of an initiator. The initiator is selected from organo-tin compounds, tin carboxylates, and tin alkoxides of the oxidation state II or IV that may contain optionally hydroxy groups. At the latest at a point in time when a desired degree of polymerization is reached, a phosphinic acid and/or a phosphinic derivative of the formula (R1)(R2)P(?O)X is added, wherein R1 and R2 each are independently of one another hydrogen, alkyl, aryl, or hetero aryl, and X is —OR3 or —NR1R2, wherein R3 is hydrogen, alkyl, aryl, MI or ½MII and MI is an alkali metal ion and MII is an alkaline earth metal ion and wherein the substituents R1 and R2 have the meaning indicated above.