diff --git a/lib/System/Win32/ThreadLocal.inc b/lib/System/Win32/ThreadLocal.inc
index b8b933c4d29..e7e3cb7ce11 100644
--- a/lib/System/Win32/ThreadLocal.inc
+++ b/lib/System/Win32/ThreadLocal.inc
@@ -44,6 +44,7 @@ void ThreadLocalImpl::setInstance(const void* d){
   DWORD* tls = static_cast<DWORD*>(data);
   int errorcode = TlsSetValue(*tls, const_cast<void*>(d));
   assert(errorcode != 0);
+  (void)errorcode;
 }
 
 void ThreadLocalImpl::removeInstance() {