Research on charter schools tends to focus on direct and immediate effects on student outcomes. However, there may be unintended indirect effects on, for example, the teacher labor market. Charter schools tend to hire teachers with fewer traditional teaching credentials, which may reduce the equilibrium quantity of teachers who have traditional credentials and seek to make teaching a career. We test whether charter entry reduces the supply of university teacher education degrees, exploiting within- and between-district variation in the timing of charter school entry in districts containing college teacher preparation programs. Applying a generalized difference-in-difference model, we find that a 10 percent increase in charter market share decreases the supply of traditionally prepared teachers by one percent per year on average. This effect is concentrated in elementary education and special education degrees, which, anecdotally, are less valued in charter schools.