Workplace safety is an important issue in global public policy. Given the failure of many governments to enforce their workplace safety laws, might voluntary programs help in this regard? Most studies on the effectiveness of voluntary programs focus on their first-order effects reflecting program goals. Yet, well-designed programs that focus on firms’ internal practices and policies can have significant spillover effects beyond the program objectives. This insight motivates our study of the second-order effect on occupational safety of ISO 9001, the most widely adopted voluntary standard in the world. While ISO 9001 is a quality management standard, the internal systems that ISO certified firms establish can improve workplace safety. This is because some workplace practices that lead to poor product quality also contribute to an unsafe working environment. Our empirical analysis covering 92 countries for the period 1993–2012 supports our argument. We find that 1 per cent increase in country-level ISO 9001 certification count is associated with 0.04 per cent decline in occupational injury rate (injury per 10,000 working population). Importantly, our finding is more pronounced where public law regarding workers’ rights is weak, suggesting that voluntary programs can fill in the governance gaps.