Under Section 23 of the Indian Contract Act, 1872, which of the following is NOT a ground on which the consideration or object of an agreement is regarded as unlawful?

Section 23 declares the consideration or object of an agreement unlawful if it is forbidden by law; or is of such a nature that, if permitted, it would defeat the provisions of any law; or is fraudulent; or involves or implies injury to the person or property of another; or the court regards it as immoral or opposed to public policy. Every agreement of which the object or consideration is unlawful is void. Inadequacy of consideration is dealt with separately under Section 25, Explanation 2, which provides that an agreement to which the consent of the promisor is freely given is not void merely because the consideration is inadequate.