diff --git a/include/winnt.h b/include/winnt.h
index 58c76e2..1aeb72a 100644
--- a/include/winnt.h
+++ b/include/winnt.h
@@ -607,6 +607,7 @@
 
 #else
 
+#undef SLIST_ENTRY /* for Mac OS */
 #define SLIST_ENTRY SINGLE_LIST_ENTRY
 #define _SLIST_ENTRY _SINGLE_LIST_ENTRY
 #define PSLIST_ENTRY PSINGLE_LIST_ENTRY