diff --git a/include/libbb.h b/include/libbb.h
index 55510316b..6e37b8d04 100644
--- a/include/libbb.h
+++ b/include/libbb.h
@@ -348,9 +348,9 @@ extern char *bb_get_last_path_component_strip(char *path) FAST_FUNC;
 /* "abc/def/" -> "" and it never modifies 'path' */
 extern char *bb_get_last_path_component_nostrip(const char *path) FAST_FUNC;
 
-int ndelay_on(int fd) FAST_FUNC;
-int ndelay_off(int fd) FAST_FUNC;
-int close_on_exec_on(int fd) FAST_FUNC;
+void ndelay_on(int fd) FAST_FUNC;
+void ndelay_off(int fd) FAST_FUNC;
+void close_on_exec_on(int fd) FAST_FUNC;
 void xdup2(int, int) FAST_FUNC;
 void xmove_fd(int, int) FAST_FUNC;
 
diff --git a/libbb/xfuncs.c b/libbb/xfuncs.c
index a02a504b0..23f27516f 100644
--- a/libbb/xfuncs.c
+++ b/libbb/xfuncs.c
@@ -25,19 +25,25 @@
 #include "libbb.h"
 
 /* Turn on nonblocking I/O on a fd */
-int FAST_FUNC ndelay_on(int fd)
+void FAST_FUNC ndelay_on(int fd)
 {
-	return fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) | O_NONBLOCK);
+	int flags = fcntl(fd, F_GETFL);
+	if (flags & O_NONBLOCK)
+		return;
+	fcntl(fd, F_SETFL, flags | O_NONBLOCK);
 }
 
-int FAST_FUNC ndelay_off(int fd)
+void FAST_FUNC ndelay_off(int fd)
 {
-	return fcntl(fd, F_SETFL, fcntl(fd, F_GETFL) & ~O_NONBLOCK);
+	int flags = fcntl(fd, F_GETFL);
+	if (!(flags & O_NONBLOCK))
+		return;
+	fcntl(fd, F_SETFL, flags & ~O_NONBLOCK);
 }
 
-int FAST_FUNC close_on_exec_on(int fd)
+void FAST_FUNC close_on_exec_on(int fd)
 {
-	return fcntl(fd, F_SETFD, FD_CLOEXEC);
+	fcntl(fd, F_SETFD, FD_CLOEXEC);
 }
 
 char* FAST_FUNC strncpy_IFNAMSIZ(char *dst, const char *src)