While some states have suggested that the cutting-edge nature of fully autonomous weapons will significantly complicate the treaty process, drafters of an instrument on the topic can look to existing international law and principles for guidance. These weapons systems present distinctive challenges, and no single source constitutes a model response, but creating new law from scratch could unnecessarily slow the progress of negotiations. International law and non-legally binding principles of artificial intelligence (AI) provide ample precedent for the elements of a new treaty. Lessons from the past can and should be adapted to this emerging technology.