Jeff, I would like to suggest to add in mqueue.h #include <sys/fcntl.h> - or - #include <fcntl.h> because mq_xxx functions may use flag definitions from there (O_CREATE, O_RDONLY, etc...). I've checked the Solaris 8 headers and they include <sys/fcntl.h> in <mqueue.h>. Regards, José Gonçalves