diff --git a/sys/sys/fd_set.h b/sys/sys/fd_set.h
index b5492b3647e0..56d807dc9f2d 100644
--- a/sys/sys/fd_set.h
+++ b/sys/sys/fd_set.h
@@ -68,11 +68,11 @@ typedef	struct fd_set {
 } fd_set;
 
 #define	FD_SET(n, p)	\
-    ((p)->fds_bits[(unsigned)(n) >> __NFDSHIFT] |= (1 << ((n) & __NFDMASK)))
+    ((p)->fds_bits[(unsigned)(n) >> __NFDSHIFT] |= (1U << ((n) & __NFDMASK)))
 #define	FD_CLR(n, p)	\
-    ((p)->fds_bits[(unsigned)(n) >> __NFDSHIFT] &= ~(1 << ((n) & __NFDMASK)))
+    ((p)->fds_bits[(unsigned)(n) >> __NFDSHIFT] &= ~(1U << ((n) & __NFDMASK)))
 #define	FD_ISSET(n, p)	\
-    ((p)->fds_bits[(unsigned)(n) >> __NFDSHIFT] & (1 << ((n) & __NFDMASK)))
+    ((p)->fds_bits[(unsigned)(n) >> __NFDSHIFT] & (1U << ((n) & __NFDMASK)))
 #if __GNUC_PREREQ__(2, 95)
 #define	FD_ZERO(p)	(void)__builtin_memset((p), 0, sizeof(*(p)))
 #else