We analyze the effect of bilateral investment treaties (BITs) on bilateral foreign portfolio investment in equity and debt securities. We find that expropriation risk and the level of a BIT's investor protection are complementary. Applying a Poisson Pseudo-Maximum-Likelihood model to a panel of 60 home and 39 host countries from 2002 to 2017, we find that host countries receive 40% more bilateral equity investment when they protect foreign investors with a BIT. This effect almost doubles when investment protection of BITs is strong, and the political risk of the host country is high.