Open source software (OSS) has increased its importance during recent years. The significance of OSS usability has been acknowledged; however, usability work, albeit carried out, doesn’t necessarily have any impact on the OSS under development. This paper examines how the impact of usability work can be increased in OSS projects. Through cross-case analysis, seven OSS development cases including usability work were examined and characteristics contributing to usability work having an impact identified. The analysis indicates that for increasing the impact of usability work, enculturation of usability specialists is important. Enculturation happens naturally when usability specialists take part in the project from the very beginning, but in OSS development this is uncommon. Otherwise, usability specialists need to place extra effort on enculturation, which in our data involved various kinds of practices relating to 1) understanding the product under development, 2) finding motivation for usability and 3) locating and targeting the decision-makers.