We show that granting migrants legal status enables climate adaptation by making extreme heat less dangerous. We study Spain's 2005 regularization program, which granted work permits to approximately 600,000 undocumented migrants. We examine its effect on heat-related hospitalizations among working-age individuals, primarily for heat strokes resulting from strenuous work in high temperatures. Our triple-difference design combines the timing of the reform, cross-provincial variation in pre-reform shares of undocumented migrants, and within-province variation in extreme heat. Following regularization, an additional day above 35C became 3.3 percentage points less likely to result in a heat-related hospitalization in exposed provinces relative to unexposed provinces, a 9.4 percent decline relative to the pre-reform mean. The evidence points to improved outside options as the main mechanism: migrant workers reallocate away from agriculture, the most heat-exposed sector. These findings indicate that labor market institutions can facilitate climate adaptation by expanding workers' access to safer jobs.