A catalyst, containing a ketone peroxide, e.g., methyl ethyl ketone peroxide, and an organic non-ketonic diperoxide, e.g., 2,5-dimethyl-2,5-bis(2-ethyl hexanoyl peroxy)hexane, is used to cure polyester resins containing over 900 p.p.m. of an inhibitor. A small amount of sodium methoxide can be used as part of the catalyst. More specifically, polyester resins containing 900 to 40,000 p.p.m. of inhibitors can be cured within 10 minutes to 24 hours with the novel catalyst.