One of the challenges that students face during the transition from high school to university is mastering discipline-specific academic expectations and norms. From a language perspective, they may encounter new academic and disciplinary vocabulary, some of which will be metaphoric in nature. However, some students whose first language is not English may struggle, as metaphoric competence is not often a consideration in ESL/EAP classrooms (Littlemore & Low, 2006). Among the supports that postsecondary institutions have implemented to improve students' chances of success are diagnostic and post-entry language assessment (Read, 2016). This mixed methods study investigated the comprehension of metaphoric language in first-year engineering reading materials using diagnostic assessment. First, a corpus of first-year engineering texts was qualitatively explored, finding personification and family/relationship metaphors. Subsequently, a metaphor comprehension test was designed using content from the corpus and administered as a reading task in an existing diagnostic assessment for first-year engineering students. Descriptive statistics, correlations, and t-test analysis of the responses revealed that English first-language (L1) students outperformed English second/additional (L2) language students. Further, those who performed poorly on the diagnostic assessment tended to also struggle with the metaphor comprehension task. Implications are discussed for EAP and first-year university classrooms.