This paper investigates how the language of instruction in Dutch higher education (Dutch versus English) affects speech production by L1 Dutch-speaking lecturers. In a pairwise design, three young lecturers that were highly proficient in English gave two comparable lectures each (L1 Dutch and L2 English). Results show that the L1 Dutch lectures were consistently given at slightly higher syllabic speech and articulation rates and that filled pauses were shorter and occurred less often in Dutch than in English lectures. In addition, L1 Dutch lectures contained a more diverse vocabulary and showed pitch patterns which have been shown to be associated with greater liveliness and higher perceived charisma of the speakers. We discuss possible reasons for the observed acoustic differences and the potential impact of our findings in the light of the ongoing transition from Dutch-medium instruction to English-medium instruction in Dutch higher education.