Don't redefine WINNT version
diff --git a/lib/zipwin32.h b/lib/zipwin32.h
index e989a0e..d2c5d82 100644
--- a/lib/zipwin32.h
+++ b/lib/zipwin32.h
@@ -35,7 +35,7 @@
 */
 
 /* 0x0501 => Windows XP; needs to be at least this value because of GetFileSizeEx */
-#ifndef MS_UWP
+#if !defined(MS_UWP) && !defined(_WIN32_WINNT)
 #define _WIN32_WINNT 0x0501
 #endif