If an illegal contract is executory, either party can enforce it.

Illegal Contract

An agreement that is either unlawful in nature or made with the purpose of undertaking an illegal act, and thus, is not enforceable by law.

Executory

Pertaining to contracts or agreements that are not yet fully performed or completed by all involved parties.

Enforce

To compel observance of or obedience to a law, rule, or obligation.