I've narrowed it down to this line in lwlib/config.h tickling the bug: #define ATHENA_H_PATH X11/Xaw The code preprocesses fine if that #define doesn't have a / in it (but of course then loses because it can't fine the header files. I'm about to report this to IBM. The truly bizzare part is this exposed ANOTHER preproccesor bug - the code would expand into *asking* for "#include <X11/Xaw/whatever.h>", but what would get *included* was "#include <X11>". It quit after the /. And yes, the preprocessor would happily suck in the directory. Gaak. I've already reported that one. /Valdis