The seminal ruling of the Court of Justice in G.K. e.a (Parquet européen) addresses one of the key elements of the EPPO Regulation which is the mechanism for cross-border cooperation between European Delegated Prosecutors (EDPs). This mechanism is designed to enable prosecutors in different Member States to cooperate in an effective manner limiting judicial authorisation for investigation measures undertaken in a certain State at the request of an EDP in a different State to one instance only (‘single judicial authorisation’). However, the wording of the EPPO Regulation is far from conclusive on this aspect Article 31 being in reality awkward compromise balancing Member States’ views on the scope of judicial review of assigned investigation measures in cross-border cases. This significant provision of the new EPPO Regulation was put to test before the national courts at the case at hand. The CJEU's ruling suggests that the notion of single judicial authorisation has been dealt a blow as we now always will have two forms of judicial control in a cross-border EPPO investigation: one prior on the merits in the State of the handling EDP and one formal in the State of the assisting EDP. In principle, the Court largely followed the Opinion by AG Ćapeta to the extent that the review conducted in the State of the assisting EDP where a measure requires judicial authorisation may relate only to matters concerning the enforcement of that measure. The CJEU judgment requires us to think more broadly on the EPPO Regulation and the potential need for EU harmonisation in this area. While the establishment of the EPPO is a welcome step towards a ‘federalisation’ of EU criminal law in the specific area of crimes against the EU budget, the EPPO cannot function effectively with some degree of harmonisation of national criminal procedures. The judgment at hand highlights the implications of this incomplete centralisation of national criminal procedures which makes it more cumbersome for the EPPO to fulfil its task of combating crimes against the EU’s financial interests effectively.