In a just-published decision of October 20, 2015 (T 1673/11 ) a Board of Appeal had to decide about the admissibility of a change in the claim category. The granted claim was drafted in the category of a Swiss-type process claim “the use of human acid alpha glucosidase in the manufacture of a medicament …” whereas the claim as maintained by the Opposition Division was in the category of a purpose-limited product claim “human acid alpha glucosidase … for use in the treatment of … disease …” The Board of Appeal has revoked the patent in its entirety, saying: “The patent according to the main request held allowable by the Opposition Division contravened Article 123(3) EPC, because the change in claim category from Swiss-type process claim in the patent as granted to purpose-limited product claim in the main request extended the protection conferred.” The decision suggests to the patentee to be extremely careful when changing the claim category.