Where mistakes occur in security documents, practitioners usually have to assess whether they should be rectified by the court, or whether rectification by the parties alone is sufficient (eg in a Deed of Rectification (DoR)). This can create particular headaches if the mistake is spotted after registration; and the consequences may also depend on the nature of the mistake. For example, if the DoR arguably creates a new security (such as by correcting a mistake in the definition of the liabilities secured), this may cause problems where the simple correction of addresses or other typographical errors might not. This article considers the law relating to rectification of such documents, and some of the practical implications of dealing with rectification whether through the courts or simply between the parties to the security.