I present a new global value chain (GVC) framework in which intermediate input suppliers produce specialized inputs that are only compatible with specific downstream uses. This feature is confirmed by firm-level data and is at odds with the current GVC approach which assumes that all products within a given industry utilize the same inputs. For example, Mexican firm-level data shows that the manufacturing firms that export to the U.S. utilize relatively more U.S. inputs than those that export to other destinations. I show how the new GVC framework can combine bilateral trade data with firm-level data in order to obtain GVC flows that reflect the heterogeneity in the use of inputs observed in the latter. This reveals that 27% of the $118bn of Mexican final good exports to the U.S. is U.S. value-added returning home. In contrast, the current GVC approach yields a share of only 17% since it ignores the specialized inputs channel. This discrepancy has serious implications for the ongoing renegotiation of NAFTA as it suggests that the potential costs of supply chain disruption are being understated. Lastly, I show how to compute these counterfactuals with an extension of the influential sufficient statistics approach to specialized inputs models and highlight important areas for future data collection.