diff --git a/gdk/gdkdragsurface.c b/gdk/gdkdragsurface.c
index 971584c042..5e41b4bbe7 100644
--- a/gdk/gdkdragsurface.c
+++ b/gdk/gdkdragsurface.c
@@ -30,6 +30,12 @@
  * during a DND operation.
  */
 
+/**
+ * GdkDragSurfaceInterface:
+ *
+ * The #GdkDragSurfaceInterface implementation is private to GDK.
+ */
+
 G_DEFINE_INTERFACE (GdkDragSurface, gdk_drag_surface, GDK_TYPE_SURFACE)
 
 static gboolean