--- 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; }