diff --git a/src/windows.hpp b/src/windows.hpp
index 4f5d246d..5e98ffb8 100755
--- a/src/windows.hpp
+++ b/src/windows.hpp
@@ -50,7 +50,8 @@
 #endif
 
 //  Workaround missing Mstcpip.h in mingw32 (MinGW64 provides this)
-#if defined __MINGW32__ && !defined SIO_KEEPALIVE_VALS && !defined __MINGW64__
+//  __MINGW64_VERSION_MAJOR is only defined when using in mingw-w64
+#if defined __MINGW32__ && !defined SIO_KEEPALIVE_VALS && !defined __MINGW64_VERSION_MAJOR
 struct tcp_keepalive {
     u_long onoff;
     u_long keepalivetime;