--- a/src/vis.h.anc	2021-09-24 22:00:03.900321816 +0200
+++ b/src/vis.h	2021-09-24 22:00:21.500028958 +0200
@@ -79,7 +79,6 @@
  */
 #define	UNVIS_END	1	/* no more characters */
 
-#include <sys/cdefs.h>
 
 __BEGIN_DECLS
 char	*vis(char *, int, int, int);
--- a/src/vis.h.anc	2021-09-24 22:05:19.543069573 +0200
+++ b/src/vis.h	2021-09-24 22:06:00.430389216 +0200
@@ -80,7 +80,9 @@
 #define	UNVIS_END	1	/* no more characters */
 
 
-__BEGIN_DECLS
+#ifdef __cplusplus
+extern "C" {
+#endif
 char	*vis(char *, int, int, int);
 int	strvis(char *, const char *, int);
 int	stravis(char **, const char *, int);
@@ -93,6 +95,8 @@
 ssize_t strnunvis(char *, const char *, size_t)
 		__attribute__ ((__bounded__(__string__,1,3)));
 
-__END_DECLS
+#ifdef __cplusplus
+}
+#endif
 
 #endif /* !HAVE_STRNVIS || BROKEN_STRNVIS */