Okla. Stat. tit. 15, § 15-64: Mistake of law defined

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.