A process of stabilizing a bidentate or tridentate phosphorus-based phosphite ester ligand or mixture thereof in a hydrocyanation reaction milieu comprising water, wherein the ligand or ligand mixture comprises one or more of (i) a bidentate biphosphite ligand of formula (III), (R12—X12) (R13—X13) P—X14—Y—X24—P(X22—R22) (X23—R23) or (ii) a tridentate triphosphite ligand of formula (IIIA) (R12—X12) (R13—X13) P—X14—Y—X32—P(X34—R34)—(X33—Y2—R24—P(X23—R23)—(X22—R22) where each X is oxygen or a bond and each Y is an optionally substituted C6-C20 arylene group, comprising admixing the bidentate and/or tridentate with a stabilizing amount of one or more monodentate phosphite ligand of formula P(X1—R1)(X2—R2)(X3—R3) where each X is oxygen or a bond, wherein the monodentate ligand has a rate of hydrolysis greater than the rate of hydrolysis of the bidentate or tridentate ligand in the presence of water in a hydrocyanation reaction milieu, and thereby preserve concentrations and proportions of the bidentate and/or tridentate ligand(s) in the ligand blend.