Understanding the proactive roles of receivers in peer feedback processes is crucial because proactive recipience carries great potential in enhancing the effectiveness of feedback and supporting self-regulated (SRL) and co-regulated learning (CoRL). However, receiver's proactivity has been insufficiently explored and the field lacks a clear understanding of how peer feedback receivers could aid academic self-regulation and co-regulation. This study unpacks the black box through examining different receiver roles in peer feedback dialogue and receiver-triggered SRL and CoRL behaviours in an undergraduate writing course for first-year English majors in China. Data were collected through audio-taped peer feedback dialogue, stimulated recall interviews and journals. Findings revealed a variety of increasingly active receiver roles: respondent, verifier, explicator, negotiator, seeker and generator. Assuming these roles, receivers not only regulated their own learning by self-monitoring works, evaluating the quality of received comments and co-producing feedback but also improved feedback providers' writing and evaluative skills. The study challenges the stereotypical image of passive receivers and argues that receiver proactivity could turn peer feedback into a mutually beneficial learning activity for receivers and providers. Implications for developing receiver proactivity are discussed.