Camera-based motion tracking has become a popular enabling technology for gestural human-computer interaction. However, the approach suffers from several limitations which have been shown to be particularly problematic when employed within musical contexts. This paper presents Leimu, a wrist mount that couples a Leap Motion optical sensor with an inertial measurement unit to combine the benefits of wearable and camera-based motion tracking. Leimu is designed, developed and then evaluated using discourse and statistical analysis methods. The results indicate that the Leimu is an effective interface for gestural music interaction and offers improved tracking precision over Leap Motion positioned on a table top.