Customer–supplier relationships have been promoted as a source of value for customers and as a way for suppliers to differentiate. Customer-perceived relationship value (i.e., a customer's overall assessment of the benefits and sacrifices of a given relationship with a supplier) is driven by relationship functions (i.e., the co\ntributions a supplier makes to a customer's value-creation processes). Earlier research categorizes relationship functions into two groups: direct, operation-related functions and indirect, change-related functions. This research finds that indirect functions have less impact than direct functions. Given the widely discussed advantages of supplier involvement in customer innovation, and the importance of information, access to market actors and motivation, this study analyzes why change-related functions have less of an impact than operation-related functions. The empirical results reveal that change-related relationship functions have a non-linear, inverted u-shaped impact on relationship value, and that the degree of customer innovativeness moderates this impact. Thus, while an analysis of all relationship functions is necessary, suppliers wishing to optimize business relationships should pay particular attention to customer innovativeness. The non-linear impact of change-related relationship functions gives rise to several interesting avenues for further research.