Compared with the vast literature on the investment and productivity effects of land rights formalization, little attention has been paid to the impact of variation in individuals’ tenure security under customary tenure regimes. This is a serious gap not only because most of Africa’s rural land is held under informal arrangements, but also because gradual erosion of long-term rights by women and migrants is often an indication of traditional systems coming under stress. Using a unique survey experiment in Malawi, the analysis shows that (i) having long-term land rights of bequest and sale has a significant impact on investment and cash crop adoption; (ii) women’s land rights of bequest and sale, joint with local institutional arrangements, can amplify the magnitude of such effects; and (iii) the effects found here can be obscured by measurement error associated with traditional approaches to survey data collection on land ownership and rights.