diff --git a/include/wx/msw/subwin.h b/include/wx/msw/subwin.h
index 9e48b9e35f..85fdb68186 100644
--- a/include/wx/msw/subwin.h
+++ b/include/wx/msw/subwin.h
@@ -152,6 +152,7 @@ private:
     {
         m_count = 0;
         m_hwnds = NULL;
+        m_ids = NULL;
     }
 
     // number of elements in m_hwnds array