Financial constraints hamper the ability of small and medium-sized enterprises (SMEs) to undertake innovative activities, which, in turn, affects countries’ long-term growth. Therefore, promoting access to external funding for SMEs represents an important challenge for policymakers. This paper investigates whether innovation subsidies, provided by France's public investment bank to French SMEs, have translated into better access to both debt and equity financing by means of a certification effect. We exploit a unique database that collates the innovation subsidies received by French firms over the 2000-2014 period to construct a quasi-natural experiment and evaluate the causal impact of these subsidies on financial constraints for SMEs. We find a significant improvement in access to bank financing for subsidized firms, but the effect is heterogeneous and mainly concentrated on micro and small firms that have been operating for around six years. In contrast, we do not find any significant improvement in access to equity financing. We demonstrate that this last result is partly explained by a substitution effect between bank debt and equity financing.