Social support has been cited as one of the most effective resources to alleviate job-related stress. The purpose of this study was to investigate the moderating effect of leader social support on the stress-strain relationship. A total of 768 workers from 45 different organizations participated in the study. The results of the moderated regression analyses showed that the effect of leader social support on the stressor-strain relationship depended on source congruence. Whereas we found a reverse buffering effect for leader support on the role conflict-strain relationship we found favorable buffering effects for leader support on the physical stressors-strain relationship. These differential buffering effects did not emerge when considering co-worker support. We discuss the implications of our results for shedding light on the mixed evidence regarding the buffering effects of social support reported in prior research.