This Article posits that the present conception of protective jurisdiction—whereby states may assert jurisdiction over extraterritorial conduct that endangers certain national security interests—fails to delimit state conduct in a manner reconcilable with general principles of international law. Protective jurisdiction’s vague formulation has enabled states to use the concept as a pretext for legislating conduct in foreign territory that bears no meaningful connection to their national security. Take the example of a recent U.S. material support of terrorism law, which asserts protective jurisdiction over a broad range of foreign conduct in support of the Basque Fatherland and Liberty organization (ETA), even though the ETA arguably does not pose a meaningful threat of harm to U.S. national security. Under the prevailing international conception of protective jurisdiction, the U.S. statute is reviewed for “reasonableness” based on comity considerations and comparative state interests. Yet, without the consent of Spain and other affected states, such cross-border regulation should be subject to a rule of international law that requires a juridical link between the extraterritorial conduct and national security. This Article proposes to standardize such a link by reformulating protective jurisdiction as a circumstance precluding wrongfulness under international law. Just as the state of necessity and self-defense doctrines indicate circumstances where otherwise internationally wrongful conduct is exceptionally permitted for the purpose of national security, this Article argues that protective, cross-border regulation should be limited to those exceptional circumstances where it is necessary to protect the regulating state from harm to an essential security interest. Only in those circumstances would a state be sufficiently connected to extraterritorial conduct to warrant interference in the domestic affairs of another state.