This research investigatesthe impact of work overload as a challenge stressor on language proficiency among non-native English teachers. It also explores the specific areas of their language that are most affected by this challenge stressor. A weekly diary was kept by one non-native English teacher at the University of Essex. The findings suggest that work overload negatively affected the participant’s fluency and pronunciation. This study extends previous findings by exploring the relationship between work overload and language proficiency through detailed diary entries. This research underscores the negative implications of work overload on language proficiency among non-native teachers. By addressing the impact of challenge stressors, such as work overload, on language proficiency, this study contributes to a deeper understanding of the complexities surrounding teacher performance in the face of high workload challenges.