This paper evaluates the appropriateness of the tax policymaking process that led to the introduction, and the later adaptation, of a tax on mobile money transactions in Uganda in 2018. We examine the unusual source of the proposal, how this particular tax diverged from the usual tax policymaking process, and whether certain key stakeholders were excluded. We argue that weaknesses in the tax policymaking process undermined the quality of policy design, and resulted in a period of costly, and avoidable, policy adjustment. This case study is relevant for Uganda as well as for other low-income countries which could be exposed to similar challenges in designing effective taxes for the mobile money industry.