--- a/include/aws/common/byte_order.inl
+++ b/include/aws/common/byte_order.inl
@@ -37,7 +37,7 @@
     }
 #if (defined(__GNUC__) || defined(__clang__)) && !defined(CBMC)
     return __builtin_bswap64(x);
-#elif defined(_MSC_VER)
+#elif defined(_WIN32)
     return _byteswap_uint64(x);
 #else
     uint32_t low = x & UINT32_MAX;
