Using the case of harm reduction drug policy in Budapest, I demonstrate how a successful drug policy was made to fail at the local and national scales, and how that failure in turn spurred the mobility of harm reduction’s implementation across scales and into the European Union’s Drugs Strategy. I show how focusing on policy failure exposes the politics of making and mobilizing urban drug policy, and how an analysis of failure can uncover unforeseen effects of the local politics of policy mobility. This paper introduces an analytic of discursive and material failure, developing a spatial grammar for analysing both the discursive framing of policies as failed and the actually existing processes and effects of failed policy. Analysing failure as both discursive and material allows scholars to break down policymaking processes into the political and practical elements assembled in policy mobilization. Discursive policy failures take into consideration the framing and accounting of actions, events and processes, while analysis of material failure begins with seemingly fewer political questions because of its focus on the technical. I argue that it is in understanding the relationship between material and discursive failure that the politics of urban policy mobility becomes a central question.