The Indonesian government's attention to economic infrastructure development has increased over the last two decades. However, there has been a trend of rampant rent-seeking in infrastructure projects by elites in both local and central governments. Nonetheless, why and how rent-seeking practices in infrastructure projects have been so endemic in Indonesian local government remains poorly understood. This article addresses this by investigating how infrastructure development in local government serves dual functions of economic growth and political commodity by utilising qualitative data obtained from interviews in Central Kalimantan (2016) and East Nusa Tenggara (2020) provinces. This data confirms the existence of infrastructure's dual function, in which official regional development planning documents and accompanying regulations are more likely to function as a legal umbrella for legalising rent-seeking practices. The term ‘unjust by default‘ identifies the practice of rent-seeking by formalising political-economic interests into regional development planning documents and manipulating regulations in order to implement infrastructure development programmes.