We argue that negative references to amicus curiae briefs in high court judgments - instances where a court explicitly signals disagreement with the legal arguments in such briefs - are a significant and understudied feature of judicial reasoning. We theorize that such references may provide courts with a tool for increasing the precision of its case law, fostering its legitimacy, and increasing compliance pressure. Our empirical analysis of the Court of Justice of the European Union indicates that negative references are used both to boost its legitimacy and to specify not only what the law is, but what it is not.