Although a court, as a judicial organ, usually fulfils its mission by resolving specific disputes brought to it, it occasionally goes beyond this simple dispute-resolving function and more actively engages in building policies which define, and “constitute,” the very polity to which the court belongs, as was seen in Brown v. Board of Education. If this “constitutional adjudication” is an integral function of any domestic high court, could (and should) an international tribunal, in particular the World Trade Organization (WTO) tribunal, also play such a distinctive role? This paper contends that the WTO tribunal has in fact assumed such role by having recently struck down a hoary antidumping practice called “zeroing” which tends to inflate dumping margins and thus is a central vehicle for contingent protection embedded in the antidumping mechanism. The paper observes that the recent proliferation of antidumping measures as a new protectionist instrument has motivated the AB’s hermeneutical departure from the past interpretation which had endorsed the practice. This, it argues, is a “constitutional” turn of the WTO which a positivist, inter-governmental mode of thinking, as is prevalent in other international organizations such as the United Nations, cannot fully expound. Critically, this turn originates from bold ideas which envision, and thus “constitute,” new institutional meaning and possibilities within the WTO. In other words, the AB’s exegesis is anchored firmly by a discernible purpose of cabining trade distortive/restrictive consequences from the use of zeroing which have long been left unchecked. Finally, WTO members, the paper maintains, must preserve the anti-zeroing jurisprudence as constitutional norms in the absence of extraordinary circumstances tantamount to a constitutional amendment. In particular, it must not be a subject of political bargaining in the trade negotiation.