EPO board of appeal rejects claim-saving approach to ambiguous amendments

Context:

• Philip Morris Products owns EP3288403, which covers a cartridge for an aerosol-generating system such as an e-cigarette. The claimed cartridge combines a storage portion for aerosol-forming substrate with a heater assembly whose heater element contains apertures of different sizes.

• Nicoventures Trading opposed the patent in September 2023. In May 2025, the EPO Opposition Division decided that the patent could be maintained only in amended form, based on Philip Morris’ second auxiliary request. Philip Morris appealed, seeking maintenance of the patent as granted or, alternatively, on the basis of earlier auxiliary requests. 

• The appeal ultimately focused on how broadly the claims should be interpreted, whether the amended wording introduced added subject matter under Article 123(2) EPC, and whether the surviving claims were novel over prior-art documents D3 and D4.

What’s new: The EPO Board of Appeal has set aside a decision maintaining Philip Morris’ e-cigarette cartridge patent only in amended form, while taking a clear position on ambiguous claim wording under Article 123(2) EPC. The Board held that an unresolved ambiguity can broaden a claim rather than being resolved in a way that preserves compliance with the added-matter rules. It found one amended manufacturing claim added subject matter, but allowed Philip Morris to delete the affected claims and remitted the case for further examination. 

Direct impact: Philip Morris lost the amended manufacturing claim as the Board’s broader interpretation brought it within subject matter not directly and unambiguously disclosed in the application as filed. However, the Board admitted a further auxiliary request deleting the affected claims and found the surviving product claim novel over D3 and D4. The case now returns to the Opposition Division for examination of inventive step and the remaining prior art, so the patent’s final scope is still unresolved. 

Wider ramifications: The decision adds to an unsettled line of EPO case law on how ambiguous claim wording should be treated when assessing added subject matter. The Board rejected the idea that ambiguity should be resolved in whichever way avoids an Article 123(2) objection, reasoning instead that an unresolved ambiguity may simply produce a broader claim interpretation. That position is particularly significant because related questions are already before the Enlarged Board in G 1/26. Until further guidance arrives, T 0977/25 gives parties another clear indication that ambiguous amendments can create added-matter risk even where one technically reasonable reading would be allowable.