The European Patent Office (EPO) has revoked one of the Broad Institute's foundational patents for CRISPR–Cas9 gene editing in eukaryotes because papers describing the technology had already been published, that is, they were in the public domain when the patent was filed. The January 17 decision is a setback to Broad and its partners, Harvard University and the Massachusetts Institute of Technology, as several of their other CRISPR–Cas9 patents could now face the same fate in Europe, resulting in a loss of royalties. The patent application was filed in December 2013, but Broad wanted to claim priority from earlier-filed US patent applications and so benefit from an effective filing date of December 2012. But the EPO determined that its strict requirements for claiming priority had been flouted, because an inventor named on the US applications from Rockefeller University was absent from the European application. This loss of priority dealt a fatal blow to the patent, since between December 2012 and December 2013, several key scientific results were published that disclosed the use of CRISPR–Cas9 gene editing in eukaryotes (Nat. Biotechnol. 31, 227–229, 2013; Science 339, 823–826, 2013), meaning that Broad's patent claims were no longer novel. Royalties aside, the overall effect of the decision may be more limited. “CRISPR technology will continue to move on quickly and, as one of the groups at the very cutting edge of the field, the Broad will continue to expand its CRISPR patent portfolio [beyond Cas9],” says Daniel Lim, an intellectual property lawyer at Allen & Overy, London. “And of course, the decision only affects the position in Europe; the Broad's key US patents are unaffected,” he adds (Nat. Biotechnol. 35, 184, 2017). Broad said it will appeal the EPO's decision on the grounds of “international inconsistency,” but this could be will be a Sisyphean task, as it would require the EPO to change its rules on claiming priority.