#define __FD_SET(d, set) ((set)->fds_bits[__FDELT(d)] |= __FDMASK(d))
#define __FD_CLR(d, set) ((set)->fds_bits[__FDELT(d)] &= ~__FDMASK(d))
-#define __FD_ISSET(d, set) ((set)->fds_bits[__FDELT(d)] & __FDMASK(d))
+#define __FD_ISSET(d, set) (!!((set)->fds_bits[__FDELT(d)] & __FDMASK(d)))
#define __FD_ZERO(set) \
((void) memset ((void *) (set), 0, sizeof (__kernel_fd_set)))