diff --git a/qemu-os-win32.h b/qemu-os-win32.h
index 6323f7f..2ff9f45 100644
--- a/qemu-os-win32.h
+++ b/qemu-os-win32.h
@@ -49,4 +49,8 @@ static inline void os_setup_post(void) {}
 static inline void os_set_line_buffering(void) {}
 static inline void os_set_proc_name(const char *dummy) {}
 
+#if !defined(EPROTONOSUPPORT)
+# define EPROTONOSUPPORT EINVAL
+#endif
+
 #endif