To date, African states have been called before 62 tribunals of the International Centre for the Settlement of Investment Disputes (ICSID); 26 cases are pending. Recently, foreign investors have invoked Bilateral Investment Treaty provisions to challenge legislation aimed at addressing historical inequalities in the distribution of natural resources in Southern Africa (Funnekotter, Piero Foresti, Border Timbers). This tension between the right to property as international investment law's origin and other rights protected by national regulation raises the question of applicable law in investor-state arbitration. The principle of "systemic integration" expressed in the Vienna Convention on the Law of Treaties requires arbitrators to have regard for the disputing parties' other relevant obligations under international law, including human rights. Such considerations are often paramount to the determination of whether expropriations are arbitrary, discriminatory, or pursued in good faith for a public purpose. In practice, however, decisions by ICSID tribunals are far from consistent in this respect. Attempts to address this through submissions made by nondisputing parties acting as amicus curiae have produced mixed results (Biwater, Border Timbers). As questions remain concerning the harmonisation of these parallel regimes, an environment of legal uncertainty is emerging which impacts negatively on local populations and investors, both current and potential. This paper argues that since the admission of the EU Commission as amicus curiae in AES v. Hungary, the door has opened for regional organisations like the Southern African Development Community to participate actively in ICSID arbitrations. This may provide an enhanced opportunity to counteract the effects of a legal regime that promotes economic and political subordination to investors and investor-states, by introducing into investment law a perspective that reflects the particular circumstances of post-colonial economies.