diff --git a/include/sys/select.h b/include/sys/select.h
index cbe35a4f..47d195f4 100644
--- a/include/sys/select.h
+++ b/include/sys/select.h
@@ -25,7 +25,7 @@ typedef struct
 #define FD_ZERO(s) do { int __i; unsigned long *__b=(s)->fds_bits; for(__i=sizeof (fd_set)/sizeof (long); __i; __i--) *__b++=0; } while(0)
 #define FD_SET(d, s)   ((s)->fds_bits[(d)/(8*sizeof(long))] |= (1UL<<((d)%(8*sizeof(long)))))
 #define FD_CLR(d, s)   ((s)->fds_bits[(d)/(8*sizeof(long))] &= ~(1UL<<((d)%(8*sizeof(long)))))
-#define FD_ISSET(d, s) ((s)->fds_bits[(d)/(8*sizeof(long))] & (1UL<<((d)%(8*sizeof(long)))))
+#define FD_ISSET(d, s) !!((s)->fds_bits[(d)/(8*sizeof(long))] & (1UL<<((d)%(8*sizeof(long)))))
 
 int select (int, fd_set *, fd_set *, fd_set *, struct timeval *);
 int pselect (int, fd_set *, fd_set *, fd_set *, const struct timespec *, const sigset_t *);