According to R. 139 EPC, linguistic errors, errors of transcription and mistakes in any document filed with the EPO may be corrected on request; however, if the request for such correction concerns the description, claims or drawings, the correction must be obvious in the sense that it is immediately evident that nothing else would have been intended than what is offered as the correction. This wording does not differ in substance from the former R. 88 EPC 1973; only some editorial changes have been made in the three languages. Hence, the jurisprudence with regard to R. 88 EPC 1973 is applicable to R. 139 EPC (T 1460/10).

Relevant for the present chapter on amendments is R. 139, second sentence, EPC, which concerns corrections to the parts of a European patent application or of a European patent relating to the disclosure (the description, claims and drawings). Other aspects related to corrections can be found under chapters II.F.4.3. "Correction of errors in a divisional application"; IV.A.5.2.2 "Correction of designation of applicant (Rule 139 EPC)"; IV.A.5.5. "Corrections under Rule 139 EPC"; IV.A.7.3. "Correction of designation of states (Rule 139 EPC)"; IV.B.3.8.2 "Correction of the withdrawal of the application under Rule 139 EPC". As to the corrections under the first sentence of R. 139 EPC, the boards of appeal, in particular the Legal Board of Appeal, have developed a large body of case law on corrections, namely that the correction must introduce what was originally intended, the error to be remedied may be an incorrect statement or an omission, and the request for correction must be filed without delay (see G 1/12, point 37 of the Reasons).