Artificial Intelligence (AI) is playing a growing role in transforming professional practices and improving processes in a variety of sectors. Many studies explore the formal uses of AI. In the public sector, AI is often used to achieve several goals, including improving the quality of public services. However, while there is already research on the formal uses of AI in the public sector, little attention has been paid to its informal use by public servants. Indeed, the latter can often resort to AI informally, including generative AI tools such as ChatGPT, to meet specific and daily needs. Through a qualitative study based on semi-directive interviews, this article explores the informal uses of ChatGPT by public servants reporting to Moroccan public establishments, shedding light on the unofficial practices of this tool. The results highlight those informal uses can be grouped into two categories: professional communication uses and specific technical uses, depending on the user profile.