The issue of retroactive transfer pricing (TP) adjustments altering customs valuation has been a long-standing question involving many multinational enterprises (MNEs). While customs authorities have traditionally ruled that upward adjustments to transfer prices should be accompanied by revisions to customs value under the transaction value method, MNEs have sought refunds in the event of downward adjustments. Realising the need for guidance, the World Customs Organisation (WCO) continues its efforts to align transfer pricing and customs valuation outcomes. However, in a recent landmark ruling, the Court of Justice of the European Union (CJEU) has affirmed that transfer prices subjected to retroactive adjustments cannot be used for customs valuation purposes under the application of the transaction value method. The ruling leaves open room for diverging interpretations and consequent uncertainties.