As the “Public Money, Public Code” movement gains steam across Europe and beyond, public administrations in Germany are increasingly curious about the potential of free and open source software. But there remains significant hesitancy: many administrations lack technical expertise and/or prior experience with FOSS, meaning they tend to struggle with fundamental questions and misconceptions about open source (for example, around the maintenance of FOSS or whether open source software is inherently less secure). One thing that can help in such cases: a trusted partner – ideally from civil society – that can help public administrations navigate these issues and which can demonstrate what the usage of FOSS in public contexts looks like in practice. The CityLAB Berlin is a public innovation lab funded by the city of Berlin and run by the non-profit Technologiestiftung Berlin that fulfills precisely such a role. Founded in 2019, the lab aims to help the city government – as well as the city as a whole – become more innovative, inclusive and resilient through the use of digital technologies and innovative methodologies. A cornerstone of its work is the promotion of open source software in public contexts: all CityLAB projects, whether websites or prototypes, are published on GitHub, including those developed in cooperation with the city government. In this talk, we’ll highlight some of the open source projects the lab has worked on (including the tree-watering platform "Gieß den Kiez", which has garnered international attention), discuss some of the reasons — both real and imagined — why public administrations struggle to integrate FOSS into their workflows, and offer ideas on what kind of concrete strategies and measures can be used to increase the acceptance and use of open source technology in public sector contexts.