This paper argues that there exists a fundamental asymmetry between relationship-specific investments (RSI) made for downstream firms (customer-specific investments – CSI) and for upstream firms (supplier-specific investments – SSI). Both types of RSI can create a hold-up problem, but everything else equal, suppliers have higher bargaining power, rendering hold-ups by suppliers more dangerous than hold-ups by customers. Using unique data on Vietnamese SMEs that allow for a clean separation between CSI and SSI, we demonstrate that this leads to less frequent SSI and that the few firms making SSI will be more risky and financially constrained. We discuss the implications of this finding for supply chain management and public policy destined to foster RSI.