Operations.h is JSC's umbrella for definitions of inline functions. If your build fails because an inline function is not defined, just #include Operations.h. Other workarounds are likely to create long-term problems. For example, including the specific BlahInlines.h file is harmful because it means that if someone moves any other inline functions out to a *Inlines.h file, they will have to potentially add that include to every .cpp file in the system that may transitively include the place where the inline function was declared. Alternatively, adding #include "Operations.h" into any other JSC headers is harmful since it risks introducing circular dependencies. The *whole point* of the *Inlines.h files that Operations.h includes is that they are never included by JSC's interface headers.