Many public organizations are challenged by demographic changes that require attention in order to safeguard all workers’ sustainable employability. This study aims to increase our understanding of how SLS-HRM practices (i.e. measures that a supervisor takes to foster an employee’s career sustainability) are linked to teachers’ employability via work-related flow, and to examine whether LMX quality moderates this relationship. SEM analyses among 698 teachers in 51 educational institutions across the Netherlands reveal that SLS-HRM practices are positively related to several dimensions of employability, through work-related flow, and that LMX quality determines the effectiveness of these practices.