Abstract This study is focused on unsustainable agri-food systems, especially intensive livestock farming and its resulting environmental harms. Specifically we focus on the development of technologies that seek to mitigate these environmental harms. These technologies are generally developed as incremental innovations in response to government regulation. Critics of these technological solutions allege that these developments legitimate unsustainable food production systems and are incapable of supporting agri-food systems transformation. At the same time, technology developers and other actors seek to present these technologies as the legitimate solution to agri-environmental harms. Our study seeks to explore the perceptions and constructions of legitimacy for technologies that are developed to reduce ammonia emissions in intensive livestock farming in Flanders (Belgium). We use a qualitative case study, employing semi-structured interviews and workshops, with technology developers of ammonia-emission reducing technologies and stakeholders in the intensive livestock farming industry in Flanders. What our study shows is that technologies developed to reduce emissions are dependent on regulative legitimacy. The normative and cognitive legitimacy of these technologies is lacking, both due to ties to the intensive livestock industry and due to uncertainty over the performance of these technologies. With the delegitimation of intensive livestock farming, the legitimacy of these technologies is also under threat. In response, technology developers are looking to (re-)construct this legitimacy through knowledge claims over the performance of their technologies. We show several ways for other actors to deal with this, centred on either re-legitimising technologies to maintain the status quo, or to contest these knowledge claims and use them to disrupt path dependencies.