Section 21 Indian Contract Act 1872
Section 21 of the Indian Contract Act 1872 is about Effect of mistakes as to law. It is under CHAPTER II of the Act. CHAPTER II is titled OF CONTRACTS, VOIDABLE CONTRACTS AND VOID AGREEMENTS.
Effect of mistakes as to law
A contract is not voidable because it was caused by a mistake as to any law in force in India; but a mistake as to a law not in force in 1 India has the same effect as a mistake of fact.
Illustration
A and B make a contract grounded on the erroneous belief that a particular debt is barred by the Indian Law of Limitation; the contract is not voidable.
See also:
Section 20 Indian Contract Act 1872 (Agreement void where both parties are under mistake as to matter of fact)