Hello, A casual boost user and abuser here. Some specifics on my OS OS X Big Sur 11.2 Xcode 12.4 Compiler clang : Apple land version 12.0.0 Boost 1.73 - forward When select_stdlib_config.hpp is included it gets to this initial code to include the file “version" ... #if defined(__cplusplus) && defined(__has_include) # if __has_include(<version>) // It should be safe to include `<version>` when it is present without checking // the actual C++ language version as it consists solely of macro definitions. // [version.syn] p1: The header <version> supplies implementation-dependent // information about the C++ standard library (e.g., version number and release date). # include <version> ... The issue is that many projects have a file “VERSION” in their top level src directory. On a traditional Linux system the case sensitivity would make sure the right file is included. However, many/most OS X file systems are case insensitive. As such, the file VERSION gets included instead. And does not compile. I have no solution to the issue but wanted to raise it. Cheers, Allen Sanderson SCI Institute University of Utah