Many mobile users rely on autocorrection mechanisms during text entry on their smartphone. Previous studies investigated the effects of autocorrection mechanisms on typing speed and accuracy but did not explore the level of frustration and perceived mental workload often associated with autocorrection. In this paper, we investigate the effect of autocorrection failures on the user’s frustration, mental and physical demand, performance, and effort using a mixed-methods user study. We identified that perceived mental and physical demand, and frustration are directly affected by autocorrection.