diff --color -U 5 -r -Z -B ./org/gtk/gtkwindow.c ./mod/gtk/gtkwindow.c
--- ./org/gtk/gtkwindow.c	2018-01-15 14:21:38.000000000 +0100
+++ ./mod/gtk/gtkwindow.c	2018-05-29 10:39:33.013711354 +0200
@@ -4151,10 +4151,18 @@
     {
       gtk_style_context_add_class (gtk_widget_get_style_context (widget), "solid-csd");
     }

   priv->client_decorated = TRUE;
+#ifdef GDK_WINDOWING_X11
+  if (GDK_IS_X11_DISPLAY (gtk_widget_get_display (widget)) && g_getenv("GTK_CSD") == FALSE)
+    {
+      gtk_style_context_remove_class (gtk_widget_get_style_context (widget), GTK_STYLE_CLASS_CSD);
+      gtk_style_context_remove_class (gtk_widget_get_style_context (widget), "solid-csd");
+      priv->client_decorated = FALSE;
+    }
+#endif
 }

 static void
 on_titlebar_title_notify (GtkHeaderBar *titlebar,
                           GParamSpec   *pspec,