Accurate self-assessment is notoriously difficult for many second language (L2) speakers as they struggle to align self-evaluations of their performance with external assessments by raters or examiners. We investigated whether a brief peer-assessment activity helps L2 speakers align their self-assessment of comprehensibility with the evaluations by external raters. We also explored how speakers’ metacognitive knowledge contributes to their self-assessments. We recorded 40 L2 English-speaking international students completing an academic oral summary task and self-assessing their speech for comprehensibility. Half of the students then performed a brief peer-assessment activity, whereas the other half engaged in a filler task before all students self-assessed their initial performance again. The speech of all students was subsequently evaluated for comprehensibility by 30 external listeners, allowing us to estimate the extent to which the students’ and the external raters’ assessments converged. Whereas engaging in peer-assessment was generally associated for L2 speakers with greater alignment between their self-ratings and external listeners’ evaluations, peer-assessment appeared to mainly benefit L2 speakers with initially good self-assessment skills. Metacognitive knowledge was not associated with greater alignment between self- and other-assessments. We discuss whether and how brief peer- and self-assessment awareness-raising activities can help L2 speakers calibrate self- and other-assessments.