Internal Fab Labs are corporate dedicated innovation entities. They attract the attention of an increasing number of firms. The literature explains it by pointing out the many benefits of implementing an internal Fab Lab, such as exploration innovation. Nevertheless, a recent study shows that most of firms fail to implement internal Labs and little is known about it. Some academics suggest that to be sustained, internal Fab Labs must be legitimate. In other words, they have to be accepted and perceived as desirable by the adopting firm. However, legitimating an internal Fab Lab could be difficult, even paradoxical as these entities allow firms to think “out of the box”, away from their norms. This exploratory research begins to fill this gap by considering the single case study of the i-Lab, the internal Fab Lab of Air Liquide. We show that legitimacy is key to support an internal Fab Lab’s implementation. In addition, we identify 3 main challenges to overcome in order to build legitimacy for such an entity: (a) the management of geographical the distance with R&D site, (b) the creation of organizational proximity with R&D units and (c) value creation.