Little research attention has been paid to whether and how working a side hustle in addition to a primary job predicts employees' interpersonal relationships with others at their main job. Drawing on social exchange theory and research on the gig economy, we investigated how an employee'ssense of achievement from a side hustle predicts relationship conflict with leaders and coworkers at their main job. We analyzed data obtained from 239 employees who had a side hustle and found that psychological entitlement mediated the link between sense of achievement from a side hustle and relationship conflict with leaders and coworkers at the main job. Competence attribution played a moderating role, strengthening the positive relationship between sense of achievement from the side hustle and psychological entitlement. Theoretical and practical implicationsfor the relationshipbetweenside hustlesand primary employment are discussed.