--- gtk+-3.16.6/gtk/gtknotebook.c.bak	2015-07-18 04:06:51.000000000 +0300
+++ gtk+-3.16.6/gtk/gtknotebook.c	2015-08-02 21:54:16.963560393 +0300
@@ -3731,9 +3731,11 @@ gtk_notebook_drag_end (GtkWidget      *w
   if (priv->detached_tab)
     gtk_notebook_switch_page (notebook, priv->detached_tab);
 
-  _gtk_bin_set_child (GTK_BIN (priv->dnd_window), NULL);
-  gtk_widget_destroy (priv->dnd_window);
-  priv->dnd_window = NULL;
+  if (priv->dnd_window) {
+    _gtk_bin_set_child (GTK_BIN (priv->dnd_window), NULL);
+    gtk_widget_destroy (priv->dnd_window);
+    priv->dnd_window = NULL;
+  }
 
   priv->operation = DRAG_OPERATION_NONE;
 }