diff --git a/physfs_internal.h b/physfs_internal.h
index d9a68a5..5d0a1b9 100644
--- a/physfs_internal.h
+++ b/physfs_internal.h
@@ -970,7 +970,8 @@ char *__PHYSFS_convertToDependent(const char *prepend,
 #define PHYSFS_LIL_ENDIAN  1234
 #define PHYSFS_BIG_ENDIAN  4321
 
-#if  defined(__i386__) || defined(__ia64__) || defined(_M_IX86) || defined(_M_IA64) || \
+#if  defined(__i386__) || defined(__ia64__) || \
+     defined(_M_IX86) || defined(_M_IA64) || defined(_M_X64) \
     (defined(__alpha__) || defined(__alpha)) || \
      defined(__arm__) || defined(ARM) || \
     (defined(__mips__) && defined(__MIPSEL__)) || \