diff --git a/acinclude.m4 b/acinclude.m4
index c7fdc2f2d..66cbdae45 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -211,7 +211,7 @@ AC_DEFUN([CURL_FUNC_GETNAMEINFO_ARGTYPES], [
 #undef inline
 #ifdef HAVE_WINDOWS_H
 #define WIN32_LEAN_AND_MEAN
-#if defined(__MINGW32__) && (_WIN32_WINNT < 0x0501)
+#if defined(__MINGW32__) && ( (!defined(_WIN32_WINNT)) || (_WIN32_WINNT < 0x0501) )
 #undef _WIN32_WINNT
 #define _WIN32_WINNT 0x0501
 #endif
diff --git a/ares/acinclude.m4 b/ares/acinclude.m4
index 4f4e6fefc..be1e4aed2 100644
--- a/ares/acinclude.m4
+++ b/ares/acinclude.m4
@@ -211,7 +211,7 @@ AC_DEFUN([CURL_FUNC_GETNAMEINFO_ARGTYPES], [
 #undef inline
 #ifdef HAVE_WINDOWS_H
 #define WIN32_LEAN_AND_MEAN
-#if defined(__MINGW32__) && (_WIN32_WINNT < 0x0501)
+#if defined(__MINGW32__) && ( (!defined(_WIN32_WINNT)) || (_WIN32_WINNT < 0x0501) )
 #undef _WIN32_WINNT
 #define _WIN32_WINNT 0x0501
 #endif