This article offers a revisionist perspective on the contested notion of Witold Lutoslawski's authenticity as a modernist composer. In doing so, it seeks to contribute to musicology's increasingly nuanced narration of the story of musical modernism. The case is argued partly by relating Lutoslawski's output to broader traditions in twentieth-century modernism, including musical representations of alienation, loss, violence, and nostalgia. Crucially, however, it is also argued by interpreting the more conventionally gratifying aspects of his pieces as something other than a hedonistic cop out. Adapting ideas from Michel Foucault, such passages are deemed heterotopian in function and interpreted in a wider-ranging sociohistorical context including Poland's responses to modernism and to Soviet Cold War oppression. The article's other main objective, therefore, is to interpret as heterotopian (and thus alternatively authentic) the expressive, structural and symbolic functions of passages in Lutoslawski's works, thereby introducing Foucault's little-known idea to a wider audience of music scholars – given the concept's potential to contribute to critical explorations of a much wider diversity of musical texts and phenomena. Analysis of Lutoslawski's Les espaces du sommeil for baritone and orchestra (1975) interconnects these strands.