Getting a Wayland surface from a GdkWindow

[Tarnyko <tarnyko tarnyko net>]

Hi folks, 

I'm trying to retrieve a Wayland surface from a GdkWindow.
Of course, I'm running GTK+3 git with native Wayland (no XWayland). 

Here's my simplified code : 

GtkWindow window = gtk_window_new (GTK_WINDOW_TOPLEVEL);
GdkWindow *w = gtk_widget_get_window (GTK_WIDGET(window));

gdk_wayland_window_set_use_custom_surface (w);
struct wl_surface *srf = gdk_wayland_window_get_wl_surface (w);
struct wl_shell_surface *ssrf = gdk_wayland_window_get_wl_shell_surface (w); 


However, Gdk keeps telling me that : 

Gdk-CRITICAL **: gdk_wayland_window_set_use_custom_surface: assertion 
'GDK_IS_WAYLAND_WINDOW (window)' failed 

What am I doing wrong ? 

Thanks for your time. 

Regards,
Tarnyko