Okla. Stat. tit. 15 § 64 : Contracts — Nature of Contracts —Consent, Duress, Fraud, Mistake, Acceptance, Revocation, Ratification — Mistake of Law TEXT PDF Mistakes of law constitute a mistake within the meaning of this article only when it arises from: 1. A misapprehension of the law by all parties, all supposing that they knew and understood it, and all making substantially the same mistake as to the law; or, 2. A misapprehension of the law by one party, of which the others are aware at the time of contracting, but which they do not rectify. Okla. Stat. tit. 15, § 64 R.L. 1910, § 909.