California Codes, Civil Code - CIV, Division 3 — Obligations, Part 2 — Contracts, Title 1 — Nature of a Contract, Chapter 3 — Consent, Section 1578
Mistake of law constitutes 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.
Notes
Defines mistake of law for this Article as either a substantially shared legal misunderstanding by all parties who believed they understood the law, or one party’s legal misunderstanding that the other parties know about when contracting but do not correct. Other legal misunderstandings are outside this definition.
Use as reference
Lexinter.net | California Code, Civil Code - CIV § 1578 | https://laws.lexinter.net/codes/california/civil-code/division-3/part-2/title-1/chapter-3/section-1578