Duterte is facing a possible complaint before the world tribunal for the thousands of killings of drug suspects during his time in office.
Though the Philippines has ratified the Rome Statute that established the ICC, Duterte said in a speech Sunday that the country never became a party to the treaty because it was never published locally as required by law, AP reported.
Duterte said because of that technical flaw, the international court can never have jurisdiction over him, "not in a million years."
Last month, an ICC prosecutor announced she was opening a preliminary examination into a complaint of suspected extrajudicial killings under Duterte's anti-drug campaign, which could amount to crimes against humanity.