This paper examines the function of 'expertise' in mediating the student-supervisor relationship in Higher Degree Research (HDR). Prevailing conceptualisations of expertise generally translate as "disciplinary acumen" and reference the supervisor's specialist disciplinary and methodological knowledge. Beyond establishing the disciplinary 'signatures' of a discipline, this expertise also confers 'symbolic capital' within the disciplinary field. This paper asks: 'What might it mean when supervisors "lack" such specific disciplinary knowledge in the supervision of HDR projects?' Drawing on theoretical foundations from Jacques Rancière and Paulo Freire, this paper considers how alternative ways of knowing and enacting scholarly inquiry might afford new terrains of practice within the HDR project, with the authors' recent experiences in supervising beyond their respective disciplinary expertise providing an illustration of this modality of supervision. This case example demonstrates how mutuality and the enactment of a dialogic supervisory approach might widen considerations of what 'counts' as expertise within HDR supervision. In setting out this conceptualisation, an ethic of mutual inquiry prefaced by Rancière's 'two wills' provides a means for activating a dynamic HDR candidature, the production of innovative research and the recognition of expertise beyond narrowly defined configurations of disciplinary acumen.