diff --git a/mingw-w64-headers/crt/stdio.h b/mingw-w64-headers/crt/stdio.h
index 4425d4b..c10202d 100644
--- a/mingw-w64-headers/crt/stdio.h
+++ b/mingw-w64-headers/crt/stdio.h
@@ -234,7 +234,7 @@
 #define __MINGW_SCANF_FORMAT  ms_scanf
 #endif
 
-#if __USE_MINGW_ANSI_STDIO
+#if __USE_MINGW_ANSI_STDIO && !defined(_CRTBLD)
 /*
  * User has expressed a preference for C99 conformance...
  */
@@ -988,7 +988,7 @@
   int __cdecl __stdio_common_vfwscanf(unsigned __int64 options, FILE *file, const wchar_t *format, _locale_t locale, va_list valist);
 #endif
 
-#if __USE_MINGW_ANSI_STDIO
+#if __USE_MINGW_ANSI_STDIO && !defined(_CRTBLD)
 /*
  * User has expressed a preference for C99 conformance...
  */
diff --git a/mingw-w64-headers/crt/stdlib.h b/mingw-w64-headers/crt/stdlib.h
index e87f639..f414f25 100644
--- a/mingw-w64-headers/crt/stdlib.h
+++ b/mingw-w64-headers/crt/stdlib.h
@@ -10,7 +10,7 @@
 #include <corecrt_wstdlib.h>
 #include <limits.h>
 
-#if __USE_MINGW_ANSI_STDIO && !defined (__USE_MINGW_STRTOX)
+#if __USE_MINGW_ANSI_STDIO && !defined (__USE_MINGW_STRTOX) && !defined(_CRTBLD)
 #define __USE_MINGW_STRTOX 1
 #endif