Okay. Sorry for adding noise. My mental hiccup was in thinking it would continue to use LOAD_WITH_ALTERED_SEARCH_PATH in conjunction with SetDefaultDllDirectories: LOAD_LIBRARY_SEARCH_DEFAULT_DIRS. I forgot that it's documented that they shouldn't be combined. Instead we have to explicitly use LOAD_LIBRARY_SEARCH_DLL_LOAD_DIR | LOAD_LIBRARY_SEARCH_DEFAULT_DIRS in each LoadLibraryExW call in order to support loading DLLs beside the extension module. In this case, embedding applications that don't call SetDefaultDllDirectories won't have a problem loading extensions that rely on AddDllDirectory. It's only ctypes and cffi packages that will be forced to update if they currently rely on PATH or the working directory.