diff --git a/dlls/ntdll/sync.c b/dlls/ntdll/sync.c
index 40b5529ff0b..5e72d3e8aca 100644
--- a/dlls/ntdll/sync.c
+++ b/dlls/ntdll/sync.c
@@ -38,6 +38,9 @@
 #include <stdlib.h>
 #include <time.h>
 
+#define NONAMELESSUNION
+#define NONAMELESSSTRUCT
+
 #include "winternl.h"
 #include "async.h"
 #include "thread.h"