diff --git a/misc/sys/cdefs.h b/misc/sys/cdefs.h
index af103fdb8a..61deb03df1 100644
--- a/misc/sys/cdefs.h
+++ b/misc/sys/cdefs.h
@@ -354,9 +354,14 @@
 /* GCC 4.3 and above allow passing all anonymous arguments of an
    __extern_always_inline function to some other vararg function.  */
 #if __GNUC_PREREQ (4,3)
+#if defined(__clang__)
+# define __va_arg_pack() __VA_ARGS__
+# define __va_arg_pack_len() 0
+#else
 # define __va_arg_pack() __builtin_va_arg_pack ()
 # define __va_arg_pack_len() __builtin_va_arg_pack_len ()
 #endif
+#endif
 
 /* It is possible to compile containing GCC extensions even if GCC is
    run in pedantic mode if the uses are carefully marked using the