The essay focuses on the application of the most-favoured-nation (MFN) treatment standard in international investment law. Investment treaties, particularly bilateral investment treaties (BITs), tend to include the MFN clause. After the 2000 decision of the ICSID arbitral tribunal concerning the Maffezini v. Spain case, other arbitral tribunals have applied the MFN clause to procedural matters, such as the observation of the so-called ‘eighteen months in domestic courts’ requirement. This application of MFN treaty clauses is debated, even if it is not consistent, as it is illustrated by the approach of the Tribunal in the Plama v. Bulgaria case. The essay analyses the relevant international practice and concludes that (re)negotiations are the best method which States might use to limit the extension of MFN treaty clauses.[...]