In an era of post-truth, the legitimacy of policy knowledge is questioned, especially in de-democratizing contexts where governments purposefully engage in post-truth politics to support their regimes. In such contexts, technocratic evidence-based policymaking is undermined, and the role played by policy advice changes. Recognizing the significance of political contextual factors that might differ across de-democratizing contexts, we analyzed how changes in policymaking and public administration in de-democratization contexts impact policy advice, focusing on think tanks in two de-democratizing countries of the European Union: Hungary and Poland. We identify four aspects of policymaking that are particularly consequential for the role of think tanks and the knowledge they produce in policymaking processes: questioning and politicizing expertise, centralizing policymaking, politicizing public administration, and dismantling accountability mechanisms. We argue that changes in policymaking along these four aspects are conducive to a controlled policy advice system, favoring short-term policy advice aligned with government ideology, while marginalizing and excluding the actors and knowledge that do not align. Our research, along with other literature on knowledge regimes in consolidated autocracies, suggests that control in these European Union-based contexts is not complete, and the think tank field continues to be characterized by diversity, particularly contestation and polarization between those who are aligned with the regime and those who oppose it. We substantiate our claims using an original interview dataset on think tanks in Hungary and Poland.