diff --git a/gtk/inspector/actions.c b/gtk/inspector/actions.c
index 339645e590..712a05fe24 100644
--- a/gtk/inspector/actions.c
+++ b/gtk/inspector/actions.c
@@ -174,6 +174,8 @@ bind_parameter_cb (GtkSignalListItemFactory *factory,
   else if (GTK_IS_ACTION_MUXER (owner))
     gtk_action_muxer_query_action (GTK_ACTION_MUXER (owner), name,
                                    NULL, (const GVariantType **)&parameter, NULL, NULL, NULL);
+  else
+    parameter = "(Unknown)";
 
   gtk_label_set_label (GTK_LABEL (label), parameter);
 }