Drawing on boundary theory, this research aims to explicate how and why flexibility idiosyncratic deals (i-deals) influence employees’ workplace behaviors. Specifically, we propose that employees provided with flexibility i-deals are more likely to need to rebuild mental connections with their work after a non-work period. Thus, flexibility i-deals are positively related to employees’ psychological reattachment to work. We further argue that psychological reattachment to work is negatively related to employees’ task performance and positively related to their workplace cyberloafing and. Taken together, we posit that flexibility i-deals tend to predict reduced task performance and increased workplace cyberloafing through the mediating role of psychological reattachment to work. Additionally, considering individual differences as a key boundary condition, we propose that perceived overqualification moderates the positive relationship between flexibility i-deals and psychological reattachment, such that the positive relationship is weaker when employees are high in perceived overqualification. By conducting two multi-wave and multi-source field studies (collective N = 439), we find support for our proposed hypotheses. Theoretical and practical implications will be discussed.