A back-door brain drain

► We study the impact of migration of unskilled workers on skill formation in the home country. ► This appears to be the least threatening scenario from the point of view of its effect on the supply of skills at home. ► We find that even without the departure of skilled workers, the home country suffers reduced aggregate skill formation. ► In the new equilibrium, the number and share of skilled workers in the home country's workforce fall. ► The combined effect is to lower the average level of human capital in the home country.