ABSTRACT In July 2018, Belgium and Tunisia signed a Memorandum of Understanding (MoU) aimed at dealing with the expulsion of irregular migrants. The MoU would have been unnoticed had it not been stipulated after the Council granted the European Commission the exclusive mandate to negotiate a European Readmission Agreement (EURA) with Tunisia. This article examines the factors that have been conducive to the post-mandate conclusion of the bilateral MoU. Approaching informalization as a systemic and evolving process in European and international relations, this article makes four contributions. First, it questions the assumption that informal deals can be equated with a political act that is unimportant or legally non-binding. Second, the article argues that the July 2018 MoU is symptomatic of unprecedented deviations, at the EU level, that today consolidate the drive for informalization. Third, the analysis shows that the MoU has been, as it were, above suspicion, for its existence has been silently tolerated as a result of broader policy developments that normalize the use of informal instruments, especially in the EU–Africa context. Fourth, beyond the official rhetoric about flexibility and informalization, the case study reveals the limits of international cooperation on readmission.