The literature on English-medium instruction (EMI) has predominantly focused on contexts where English is not the first language. Little is known about EMI in traditional English-speaking (Anglophone) contexts like Australia, where English is the first language. The highly internationalised Australian higher education has witnessed a growing cohort of foreign-born students and academics, many from non-native English-speaking backgrounds (NESB). Whilst the issue of EMI for NESB students has received increased attention, the EMI-related challenges facing NESB academics have been overlooked. This paper explores communicative and pedagogical challenges and associated strategies of NESB academics as they revealed untold stories about their teaching experiences in this EMI context. It adopts a Vygotsky's socio-cultural theoretical perspective in conceptualising English as a tool academics appropriate to mediate their teaching. A modified EMI competence framework further elaborates the use of English as a pedagogical and communicative tool. Data were generated through individual interviews and survey questionnaire with NESB academics at an Australian university. Findings revealed multiple challenges facing the academics and strategies they applied to adapt English, as a mediational tool, to effectively mediate their teaching. The study has implications for EMI research in Anglophone contexts and professional development and institutional support for NESB academics.