Since the outbreak of the Syrian armed conflict in 2012 many Western States have become concerned by the perceived rising threat of returning foreign fighters. In an effort to address this national security concern, in 2014 the Norwegian Ministry of Justice proposed an amendment to the Norwegian Penal Code. This bill, meanwhile adopted, criminalizes foreign fighters’ participation in armed conflict. The article explores the challenges and controversies raised by this piece of legislation. In particular the article uses the example of counterterrorism laws and conventions to demonstrate the potential unintended effect legal instruments can have on the robustness of the IHL regime. The article concludes by suggesting that foreign fighter laws should define and criminalize participation in armed conflict based on the act itself and the means and methods used (rather than the legal status of the person in question or on the political cause in the name of which the attack was launched).