Welfare service experiences are known to shape citizens' trust in public institutions and their sup-port of the welfare state. But, there is poor understanding of how this relationship is shaped in systems of mixed provision, that is, welfare states that use public in-house as well as contracted private providers for publically funded services. Drawing on the notion of system trust this article provides a theoretical account of how mixed-provision welfare systems condition the relationship between service experience and trust, affecting the legitimacy of the state. Utilizing a random-ized vignette experiment with participants in a general citizen survey in Sweden, we investigate whether it matters for the formation of institutional trust if the welfare service is provided by a public or third-party private provider. The main result show that the spillover of trust from positive service experiences with the provider to trust in public institutions is higher in cases of public ser-vice provision. Thus, the possibility of using welfare services to build trust in the welfare system seems to be greater when public provision is used.