Where a mistake relates to a written document there are two special remedies: non est factum and rectification.

Non est factum

As a general rule, a person who signs a contractual document is bound by it, regardless of whether he or she has read or understood it (L’Estrange v Graucob (1934). However, where a person signs a document believing it to be something totally different from what it actually was, the common law remedy of non est factum (Latin for ‘this is not my deed’) may make the contract void. In order to do this, the person seeking the remedy must prove three things:

  • That the signature was induced by a trick or fraud;
  • That they made a fundamental mistake as to the nature of the document; and
  • That they were not careless in signing it.

The mistake made by the signer must concern the actual nature of the document, not just its legal effect. Lord Reid stated in the case of Saunders v Anglia Building Society (1971) that the plea (non est factum) cannot be available to anyone who was content to sign without taking the trouble to find out at least the general effect of the document …… the essence of the plea non est factum is that the person signing believed that the document he signed had one character or one effect, whereas in fact its character or effect was quite different. He could not have such a belief unless he had taken steps or had been given information which gave him some grounds for his belief. The amount of information he must have and the sufficiency of the particularity of his belief must depend on the circumstances of each case.


Where some aspect of a written document is alleged not to reflect accurately the will of the parties, the equitable remedy of rectification may in certain circumstances allow the written document to be altered so that it coincides with the true agreement of the parties. In order for this remedy to be applied, three conditions must be satisfied:

  • The parties must have agreed about the point in question,
  • Their agreement on that aspect of the contract must have continued unchanged up to the time it was put into writing, and
  • The written document must fail to express the parties’ agreement on that point.

If all three conditions are satisfied, equity will rectify the written document, and order specific performance of the rectified document.

Rectification is an exception to the parol evidence rule, as oral evidence can be admitted in order to show that the written document is in error.

Rectification will not be available where the written document accurately records the agreement, but the agreement is based upon a mistake.

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