diff --git a/include/sys/select.h b/include/sys/select.h
index b3bab1d5..8982f39b 100644
--- a/include/sys/select.h
+++ b/include/sys/select.h
@@ -24,9 +24,9 @@ typedef struct {
 } fd_set;
 
 #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_SET(d, s)   ((s)->fds_bits[((unsigned int)d)/(8*sizeof(long))] |= (1UL<<(((unsigned int)d)%(8*sizeof(long)))))
+#define FD_CLR(d, s)   ((s)->fds_bits[((unsigned int)d)/(8*sizeof(long))] &= ~(1UL<<(((unsigned int)d)%(8*sizeof(long)))))
+#define FD_ISSET(d, s) !!((s)->fds_bits[((unsigned int)d)/(8*sizeof(long))] & (1UL<<(((unsigned int)d)%(8*sizeof(long)))))
 
 int select (int, fd_set *__restrict, fd_set *__restrict, fd_set *__restrict, struct timeval *__restrict);
 int pselect (int, fd_set *__restrict, fd_set *__restrict, fd_set *__restrict, const struct timespec *__restrict, const sigset_t *__restrict);