diff --git a/gtk/gtkcellarea.h b/gtk/gtkcellarea.h
index f857e19ab5..874a863c2b 100644
--- a/gtk/gtkcellarea.h
+++ b/gtk/gtkcellarea.h
@@ -60,6 +60,7 @@ typedef void    (*GtkCellCallback)     (GtkCellRenderer  *renderer,
 
 struct _GtkCellArea
 {
+  /*< private >*/
   GInitiallyUnowned parent_instance;
 
   GtkCellAreaPrivate *priv;
diff --git a/gtk/gtkcellareabox.h b/gtk/gtkcellareabox.h
index caba7cd4ea..a6d3a061bb 100644
--- a/gtk/gtkcellareabox.h
+++ b/gtk/gtkcellareabox.h
@@ -45,6 +45,7 @@ typedef struct _GtkCellAreaBoxPrivate       GtkCellAreaBoxPrivate;
 
 struct _GtkCellAreaBox
 {
+  /*< private >*/
   GtkCellArea parent_instance;
 
   GtkCellAreaBoxPrivate *priv;
@@ -52,6 +53,7 @@ struct _GtkCellAreaBox
 
 struct _GtkCellAreaBoxClass
 {
+  /*< private >*/
   GtkCellAreaClass parent_class;
 
   /* Padding for future expansion */
diff --git a/gtk/gtkcellareacontext.h b/gtk/gtkcellareacontext.h
index 549977f351..2731a73db4 100644
--- a/gtk/gtkcellareacontext.h
+++ b/gtk/gtkcellareacontext.h
@@ -44,6 +44,7 @@ typedef struct _GtkCellAreaContextClass         GtkCellAreaContextClass;
 
 struct _GtkCellAreaContext
 {
+  /*< private >*/
   GObject parent_instance;
 
   GtkCellAreaContextPrivate *priv;