When is it modernism? This article poses this question to traditionally based Indonesian musik kontemporer, as an occasion to examine a distinctive instance of musical modernism, but most importantly to illuminate issues with the question itself. Taking it literally, I identify when musik kontemporer was most clearly modernist, recognizing that modernism, and its conception of history, itself has a history. Scrutinizing the question's more usual goal of drawing a distinction between that which is and is not modernist, I show how the case of Rahayu Supanggah – a musician with a deep and primary commitment to the traditional performing arts, whose work has been shaped by his adoption of modernist ways of thinking without being fully defined by them – defies a simple answer. Ultimately, the article is concerned with what is at stake when invoking modernism, and what this means for the larger project of understanding musical modernism as a global phenomenon.