In its latest decision, G1/10, the Enlarged Board of Appeals of the EPO dealt with the issue of the correction of mistakes by the patentee after grant.   Sometimes a mistake in a patent document – description, claims or drawings – is discovered only after the end of the examination proceedings. If the mistake affects the claims, this may have serious consequences for the patent if it introduces an amendment that does not have basis in the application as filed. Indeed, such amendment is a ground for revocation that can - and normally will - be raised during opposition. The patentee has only very limited options to correct such a mistake, as a request for correction requires that both the mistake and its correction be obvious for the skilled person. Further, claim amendment during opposition is possible only insofar as it does not extend the protection conferred by the patent. As a consequence, the patentee may be in a position where a feature cannot remain in the claim because it does not have basis in the application as filed, but cannot be cancelled as this would extend the protection conferred by the claim. Unless the feature can be replaced by another feature having basis in the application as filed, so as not to extend claim scope, the patent will be revoked.   In the present case, the patentee had amended claim 1 during prosecution by introducing a feature comprising the term “position” which was not disclosed in the application as filed. According to the patentee, the term should have in fact read “portion”, but was inadvertently changed to ‘position’ due to a typing error.  After grant, an opposition was filed based on the grounds that the above amendment was inadmissible as the feature introduced did not have basis in the application as filed. In response, the patentee requested correction under Rule 139 EPC, which allows correction of errors in documents filed at the EPO. However, such a request requires that both the mistake and its correction are obvious to the skilled person. The patentee thus also requested correction instead under Rule 140 EPC, which allows the correction of errors in decisions of the EPO and which does not explicitly require the correction of the mistake to be obvious. As Rule 140 does not explicitly specify to whom such a request is open, nor the applicable time limit, the question was submitted to the Enlarged Board of Appeal, who held that Rule 140 EPC is not available for correction of the description, claims or drawings at the request of the patentee, including after initiation of opposition proceedings. Access: here. The decision illustrates the possible fatal consequences of the strict EPO policy with regard to amendments. Any amendment of the claims of a granted patent which does not have basis in the application as filed may lead to revocation of the patent in opposition proceedings, even if it is simply the result of a typing mistake. This is why amendments made during examination are the object of special scrutiny by Opponents. It is thus most important for Applicants to carefully review amendments filed during examination, and in particular the text proposed for grant annexed to the communication under Rule 71(3) EPC.  Writer : Simone Kling   