diff --git a/src/core/window.c b/src/core/window.c
index b7894ecbb..8b8c8aad5 100644
--- a/src/core/window.c
+++ b/src/core/window.c
@@ -1305,6 +1305,7 @@ _meta_window_shared_new (MetaDisplay         *display,
                       "Putting window %s on same workspace as parent %s\n",
                       window->desc, window->transient_for->desc);
 
+          g_warn_if_fail (!window->transient_for->override_redirect);
           set_workspace_state (window,
                                should_be_on_all_workspaces (window->transient_for),
                                window->transient_for->workspace);