Ross v Henderson [1977] 2 NZLR 458 is a cited case in New Zealand regarding illegal contracts that were later upheld that the Illegal Contracts Act 1970 had the power to validate (i.e. make legal) despite the fact that another legal enactment "deemed to be unlawful and shall have no effect".

As leases of 3 years or more are legally required to be registered with the Land Transfer Office, Henderson duly registered the lease, which included the option to purchase.

Unfortunately, the LTO standard declaration form, required under the law, was not designed for such a transaction, and later resulted in Henderson to of breached the law by not registering his purchase, making the sale illegal and of no effect.

In this background, in 1974 Ross's solicitor wrote to Henderson informing him that the sale of the farm had now come to an end.

Henderson filed in court for relief under the Illegal Contracts Act by having the sale agreement validated.