diff --git a/io/bits/fcntl2.h b/io/bits/fcntl2.h
index 34f05d793d..e29f842246 100644
--- a/io/bits/fcntl2.h
+++ b/io/bits/fcntl2.h
@@ -32,6 +32,8 @@ extern int __REDIRECT (__open_2, (const char *__path, int __oflag),
 extern int __REDIRECT (__open_alias, (const char *__path, int __oflag, ...),
 		       open64) __nonnull ((1));
 #endif
+
+#ifdef __va_arg_pack_len
 __errordecl (__open_too_many_args,
 	     "open can be called either with 2 or 3 arguments, not more");
 __errordecl (__open_missing_mode,
@@ -58,12 +60,34 @@ open (const char *__path, int __oflag, ...)
 
   return __open_alias (__path, __oflag, __va_arg_pack ());
 }
+#elif __fortify_use_clang
+__fortify_function_error_function __attribute_overloadable__ int
+open (const char *__path, int __oflag, mode_t __mode, ...)
+     __fortify_clang_unavailable ("open can be called either with 2 or 3 arguments, not more");
+
+__fortify_function __attribute_overloadable__ int
+open (__fortify_clang_overload_arg (const char *, ,__path), int __oflag)
+     __fortify_clang_prefer_this_overload
+     __fortify_clang_error (__OPEN_NEEDS_MODE (__oflag),
+			    "open with O_CREAT or O_TMPFILE in second argument needs 3 arguments")
+{
+  return __open_2 (__path, __oflag);
+}
+
+__fortify_function __attribute_overloadable__ int
+open (__fortify_clang_overload_arg (const char *, ,__path), int __oflag,
+      mode_t __mode)
+{
+  return __open_alias (__path, __oflag);
+}
+#endif
 
 
 #ifdef __USE_LARGEFILE64
 extern int __open64_2 (const char *__path, int __oflag) __nonnull ((1));
 extern int __REDIRECT (__open64_alias, (const char *__path, int __oflag,
 					...), open64) __nonnull ((1));
+# ifdef __va_arg_pack_len
 __errordecl (__open64_too_many_args,
 	     "open64 can be called either with 2 or 3 arguments, not more");
 __errordecl (__open64_missing_mode,
@@ -90,6 +114,27 @@ open64 (const char *__path, int __oflag, ...)
 
   return __open64_alias (__path, __oflag, __va_arg_pack ());
 }
+# elif __fortify_use_clang
+__fortify_function_error_function __attribute_overloadable__ int
+open64 (const char *__path, int __oflag, mode_t __mode, ...)
+     __fortify_clang_unavailable ("open64 can be called either with 2 or 3 arguments, not more");
+
+__fortify_function __attribute_overloadable__ int
+open64 (__fortify_clang_overload_arg (const char *, ,__path), int __oflag)
+     __fortify_clang_prefer_this_overload
+     __fortify_clang_error (__OPEN_NEEDS_MODE (__oflag),
+			    "open64 with O_CREAT or O_TMPFILE in second argument needs 3 arguments")
+{
+  return __open64_2 (__path, __oflag);
+}
+
+__fortify_function __attribute_overloadable__ int
+open64 (__fortify_clang_overload_arg (const char *, ,__path), int __oflag,
+	mode_t __mode)
+{
+  return __open64_alias (__path, __oflag);
+}
+# endif
 #endif
 
 
@@ -108,6 +153,8 @@ extern int __REDIRECT (__openat_alias, (int __fd, const char *__path,
 					int __oflag, ...), openat64)
      __nonnull ((2));
 # endif
+
+# ifdef __va_arg_pack_len
 __errordecl (__openat_too_many_args,
 	     "openat can be called either with 3 or 4 arguments, not more");
 __errordecl (__openat_missing_mode,
@@ -134,6 +181,28 @@ openat (int __fd, const char *__path, int __oflag, ...)
 
   return __openat_alias (__fd, __path, __oflag, __va_arg_pack ());
 }
+# elif __fortify_use_clang
+__fortify_function_error_function __attribute_overloadable__ int
+openat (int __fd, const char *__path, int __oflag, mode_t __mode, ...)
+     __fortify_clang_unavailable ("openat can be called either with 3 or 4 arguments, not more");
+
+__fortify_function __attribute_overloadable__ int
+openat (int __fd, __fortify_clang_overload_arg (const char *, ,__path),
+	int __oflag)
+     __fortify_clang_prefer_this_overload
+     __fortify_clang_error (__OPEN_NEEDS_MODE (__oflag),
+			    "openat with O_CREAT or O_TMPFILE in third argument needs 4 arguments")
+{
+  return __openat_2 (__fd, __path, __oflag);
+}
+
+__fortify_function __attribute_overloadable__ int
+openat (int __fd, __fortify_clang_overload_arg (const char *, ,__path),
+	int __oflag, mode_t __mode)
+{
+  return __openat_alias (__fd, __path, __oflag);
+}
+# endif
 
 
 # ifdef __USE_LARGEFILE64
@@ -147,6 +216,7 @@ __errordecl (__openat64_too_many_args,
 __errordecl (__openat64_missing_mode,
 	     "openat64 with O_CREAT or O_TMPFILE in third argument needs 4 arguments");
 
+#  ifdef __va_arg_pack_len
 __fortify_function int
 openat64 (int __fd, const char *__path, int __oflag, ...)
 {
@@ -168,5 +238,27 @@ openat64 (int __fd, const char *__path, int __oflag, ...)
 
   return __openat64_alias (__fd, __path, __oflag, __va_arg_pack ());
 }
+# elif __fortify_use_clang
+__fortify_function_error_function __attribute_overloadable__ int
+openat64 (int __fd, const char *__path, int __oflag, mode_t __mode, ...)
+     __fortify_clang_unavailable ("openat64 can be called either with 3 or 4 arguments, not more");
+
+__fortify_function __attribute_overloadable__ int
+openat64 (int __fd, __fortify_clang_overload_arg (const char *, ,__path),
+	  int __oflag)
+     __fortify_clang_prefer_this_overload
+     __fortify_clang_error (__OPEN_NEEDS_MODE (__oflag),
+			    "openat64 with O_CREAT or O_TMPFILE in third argument needs 4 arguments")
+{
+  return __openat64_2 (__fd, __path, __oflag);
+}
+
+__fortify_function __attribute_overloadable__ int
+openat64 (int __fd, __fortify_clang_overload_arg (const char *, ,__path),
+	  int __oflag, mode_t __mode)
+{
+  return __openat64_alias (__fd, __path, __oflag);
+}
+#  endif
 # endif
 #endif
diff --git a/io/fcntl.h b/io/fcntl.h
index 9cee0b5900..38aa12d7f2 100644
--- a/io/fcntl.h
+++ b/io/fcntl.h
@@ -337,8 +337,7 @@ extern int posix_fallocate64 (int __fd, off64_t __offset, off64_t __len);
 
 
 /* Define some inlines helping to catch common problems.  */
-#if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function \
-    && defined __va_arg_pack_len
+#if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function
 # include <bits/fcntl2.h>
 #endif
 
diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index 62507044c8..6b03417453 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -257,7 +257,9 @@
 
 # define __fortify_clang_warning(__c, __msg) \
   __attribute__ ((__diagnose_if__ ((__c), (__msg), "warning")))
-# define __fortify_clang_warning_only_if_bos0_lt(n, buf, complaint) \
+#  define __fortify_clang_error(__c, __msg) \
+  __attribute__ ((__diagnose_if__ ((__c), (__msg), "error")))
+#  define __fortify_clang_warning_only_if_bos0_lt(n, buf, complaint) \
   __attribute__ ((__diagnose_if__ \
 		  (__fortify_clang_bosn_args (__bos0, n, buf, 1, complaint))))
 # define __fortify_clang_warning_only_if_bos0_lt2(n, buf, div, complaint) \
@@ -270,6 +272,11 @@
   __attribute__ ((__diagnose_if__ \
 		  (__fortify_clang_bosn_args (__bos, n, buf, div, complaint))))
 
+#  define __fortify_clang_prefer_this_overload \
+  __attribute__ ((enable_if (1, "")))
+#  define __fortify_clang_unavailable(__msg) \
+  __attribute__ ((unavailable(__msg)))
+
 # if __USE_FORTIFY_LEVEL == 3
 #  define __fortify_clang_overload_arg(__type, __attr, __name) \
   __type __attr const __fortify_clang_pass_dynamic_object_size __name
