diff --git a/include/msvcrt/corecrt.h b/include/msvcrt/corecrt.h
index 4dc2ca53208..bec9c8911c2 100644
--- a/include/msvcrt/corecrt.h
+++ b/include/msvcrt/corecrt.h
@@ -122,18 +122,6 @@
 # endif
 #endif
 
-#if (defined(__x86_64__) || (defined(__aarch64__) && __has_attribute(ms_abi))) && defined (__GNUC__)
-# include <stdarg.h>
-# undef va_list
-# undef va_start
-# undef va_end
-# undef va_copy
-# define va_list __builtin_ms_va_list
-# define va_start(list,arg) __builtin_ms_va_start(list,arg)
-# define va_end(list) __builtin_ms_va_end(list)
-# define va_copy(dest,src) __builtin_ms_va_copy(dest,src)
-#endif
-
 #ifndef WINAPIV
 # if defined(__arm__) && defined (__GNUC__) && !defined(__SOFTFP__) && !defined(__MINGW32__) && !defined(__CYGWIN__)
 #  define WINAPIV __attribute__((pcs("aapcs")))
diff --git a/include/msvcrt/vadefs.h b/include/msvcrt/vadefs.h
index 2a612fc055c..462c2d6815f 100644
--- a/include/msvcrt/vadefs.h
+++ b/include/msvcrt/vadefs.h
@@ -27,7 +27,15 @@
 #define _ADDRESSOF(v) (&(v))
 #endif
 
-#if defined(__GNUC__) || defined(__clang__)
+#if defined (__GNUC__) && (defined(__x86_64__) || (defined(__aarch64__) && __has_attribute(ms_abi)))
+
+typedef __builtin_ms_va_list va_list;
+#define _crt_va_start(v,l)  __builtin_ms_va_start(v,l)
+#define _crt_va_arg(v,l)    __builtin_va_arg(v,l)
+#define _crt_va_end(v)      __builtin_ms_va_end(v)
+#define _crt_va_copy(d,s)   __builtin_ms_va_copy(d,s)
+
+#elif defined(__GNUC__) || defined(__clang__)
 
 typedef __builtin_va_list va_list;
 #define _crt_va_start(v,l)  __builtin_va_start(v,l)