The head of the African Development Bank is calling for an end to loans given in exchange for the continent’s rich supplies of oil or critical minerals used in smartphones and electric car batteries.

“They are just bad, first and foremost, because you can’t price the assets properly,” Akinwumi Adesina said in an interview with The Associated Press in Lagos, Nigeria, last week. “If you have minerals or oil under the ground, how do you come up with a price for a long-term contract? It’s a challenge.”

Linking future revenue from natural resource exports to loan paydowns is often touted as a way for recipients to get financing for infrastructure projects and for lenders to reduce the risk of not getting their money back.