diff --git a/extmod/moduplatform.h b/extmod/moduplatform.h
index d911d33ddd..42ed4de248 100644
--- a/extmod/moduplatform.h
+++ b/extmod/moduplatform.h
@@ -37,7 +37,7 @@
 
 #if defined(__ARM_ARCH)
 #define MICROPY_PLATFORM_ARCH   "arm"
-#elif defined(__x86_64__) || defined(_WIN64)
+#elif defined(__x86_64__) || defined(_M_X64)
 #define MICROPY_PLATFORM_ARCH   "x86_64"
 #elif defined(__i386__) || defined(_M_IX86)
 #define MICROPY_PLATFORM_ARCH   "x86"