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BGH rules that patents containing "added subject-matter" may be valid

In European patent prosecution, a patent that claims a feature that is not clearly  and unambiguously based on the original disclosure is caught in a trap and is irretrievably invalid. The trap is this: the patent must be amended to excise the added subject matter, but to do so would broaden the claims, which is not permitted, so the patent must be revoked. The German Federal Supreme Court has now ruled that there can be an escape route from the trap.

In its decision Winkelmesseinrichtung (Xa ZB 14/09), the Supreme Court has ruled that the newly added feature may remain in the claim if it serves to specify (restrict or limit) a feature disclosed as part of the invention in the original application. The escape route does not apply to a feature relating to a newly introduced technical aspect (i.e. a technical aspect not disclosed as part of the invention in the original application) notwithstanding that it restricts the scope of the claim. The question of whether an added feature renders a claim invalid depends on whether the feature results in a different invention than the one originally disclosed (a so-called aliud).

The case in question did not benefit from the escape route. The invention related to an angle measuring device comprising a housing with an opening and a clearance for receiving the sheath of a cable. According to the original application, the clearance was arranged within the housing.  However, the amended claims instead recited that the clearance was arranged within the opening (of the housing).  The BGH indicated that this was considered more than a "mere specification" of a feature disclosed in the original application.  It was an unallowable "aliud". (The BGH referred the case back to the Patents Court).

Had the amendment consisted in adding the feature that the clearance was arranged within the housing adjacent the opening, for example, it would probably have been considered a "mere specification" of a feature disclosed in the original application.  However, the amendment added a new aspect, viz. a clearance potentially outside the housing.

Of course even if the added feature can remain in the claim, no rights may be derived from it, e.g. it cannot be used to distinguish from the prior art.

The decision deviates from the current approach by the EPO as laid down in the decision Enlarged Board of Appeal decision G 1/93.

According to that decision an undisclosed added feature does not lead to revocation of the patent only if the feature restricts the scope of the claims and makes no technical contribution to the claimed invention.  Thus, in the above example, if the arrangement of the clearance within the housing adjacent the opening made any technical contribution, the amendment would not be allowable under EPO practice.


In European patent prosecution applicants must be careful not to add features to the claims that find no clear and unambiguous basis in the application as originally filed.  It is all too easy to inadvertently add matter when amending claims.  The EPO is very strict on this point.  Now the BGH confirms that the more practical approach hitherto applied in courts in Germany shall apply.  This is good for patent owners litigating in Germany.