Welcome to the new version of the Patents Manual. Please note there are changes to the numbering and sequence of the chapters and pages in the manual. You are encouraged to take the time to explore and familiarise yourself with this new structure.

6.1.17 Rule 91 Obvious Mistakes in Documents

Date Published

Rule 91.1 provides that obvious mistakes may be rectified. Where a request for rectification in respect of any document other than the Request form is submitted to the International Searching Authority, PCT Unit will action the request for rectification in ePCT. Once processed the request will appear in RIO, PCT unit will then contact the relevant examiner to alert them of the request. [Rule 91.1Ad. Inst. 511 PCT/GL/ISPE/12 at Chapter 8]

Any request for rectification from the applicant will be in the form of a letter. However, the PCT Unit, acting as the RO, can also forward replacement sheets to the search examiner for consideration under Rule 91; e.g. where the applicant has supplied a replacement sheet for another reason (e.g. to correct a defect) and the PCT Unit believes that it contains additional matter.

The search examiner considers whether the mistake is rectifiable under Rule 91.1, and completes form PCT/ISA/217 (see Annex J to this part).


  • Rule 91.1(c) to (g) is the only source of instruction when considering requests for rectification, i.e., case law does not exist.
  • Although Rule 91.1(h) allows the ISA to invite rectifications (form PCT/ISA/216), it is not envisaged that such invitations will be issued since any error which can be rectified under Rule 91 will not cause any problems in establishing the search report.
  • Authorisation of rectifications is determined solely by Rule 91.3(a) and (b) while Rule 91.1(c) determines if they are of effect. Whether such rectifications can be effective is not a consideration in authorizing and thus of no examiner concern. [Rule 91.1(c) to (g), Rule 91.3(c)]

Obvious Mistake

Mistakes which are due to the fact that something other than what was obviously intended was included in the contents of the international application may usually be rectified.  The mistake must be “obvious” in the sense that it is immediately apparent:

i. that a mistake has occurred; and

ii. that anyone would immediately recognise that nothing else could have been intended other than the rectification requested by the applicant.

Examples of obvious mistakes that are rectifiable include linguistic mistakes, spelling mistakes and grammatical mistakes so long as the meaning of the disclosure does not change upon entry of the rectification.  Mistakes in chemical or mathematical formulae would not generally be rectifiable unless the correct formulae would be common knowledge to anyone.

If a rectification is not of this nature (for example, if it involves cancellation of claims, omission of passages in the description or omission of certain drawings), it should be treated as an amendment under Article 19/34 and dealt with on that basis.

Amended Reasons

Amended Reason Date Amended

Published for testing

Back to top