This study explores why temporary agency workers are disadvantaged compared to regular workers regarding their employment-related and social rights in Belgium despite extensive equal rights regulation. Fifteen in-depth interviews among temporary agency workers were analysed thematically. The enforceability of rights poses the main problem in temporary agency workers’ disadvantaged position. The following manifestations of a lack of enforceability are discussed: (1) lack of enforceability due to ignorance and indifference about rights; (2) vulnerability hindering enforceability; and (3) lack of enforceability due to misuse by employers and cutting corners. It is argued that this problem of enforceability is mainly caused by a lack of a clear allocation of responsibilities as to who should ensure the rights of temporary agency workers.