diff --git a/lib/filterx/filterx-object.h b/lib/filterx/filterx-object.h
index 1677e44a9..418f3ab98 100644
--- a/lib/filterx/filterx-object.h
+++ b/lib/filterx/filterx-object.h
@@ -53,6 +53,7 @@ struct _FilterXType
   gboolean (*repr)(FilterXObject *self, GString *repr);
   gboolean (*len)(FilterXObject *self, guint64 *len);
   FilterXObject *(*add)(FilterXObject *self, FilterXObject *object);
+  void (*make_readonly)(FilterXObject *self);
   void (*free_fn)(FilterXObject *self);
 };
 
@@ -86,7 +87,6 @@ struct _FilterXObject
    */
   guint modified_in_place:1, readonly:1, weak_referenced:1;
   FilterXType *type;
-  void (*make_readonly)(FilterXObject *self);
 };
 
 FilterXObject *filterx_object_getattr_string(FilterXObject *self, const gchar *attr_name);
@@ -117,8 +117,8 @@ filterx_object_is_type(FilterXObject *object, FilterXType *type)
 static inline void
 filterx_object_make_readonly(FilterXObject *self)
 {
-  if (self->make_readonly)
-    self->make_readonly(self);
+  if (self->type->make_readonly)
+    self->type->make_readonly(self);
 
   self->readonly = TRUE;
 }
diff --git a/lib/filterx/object-json-array.c b/lib/filterx/object-json-array.c
index dd96fe6d4..87119101d 100644
--- a/lib/filterx/object-json-array.c
+++ b/lib/filterx/object-json-array.c
@@ -259,7 +259,6 @@ filterx_json_array_new_sub(struct json_object *jso, FilterXObject *root)
   FilterXJsonArray *self = g_new0(FilterXJsonArray, 1);
   filterx_list_init_instance(&self->super, &FILTERX_TYPE_NAME(json_array));
 
-  self->super.super.make_readonly = _make_readonly;
   self->super.get_subscript = _get_subscript;
   self->super.set_subscript = _set_subscript;
   self->super.append = _append;
@@ -381,4 +380,5 @@ FILTERX_DEFINE_TYPE(json_array, FILTERX_TYPE_NAME(list),
                     .clone = _clone,
                     .list_factory = filterx_json_array_new_empty,
                     .dict_factory = filterx_json_object_new_empty,
+                    .make_readonly = _make_readonly,
                    );
diff --git a/lib/filterx/object-json-object.c b/lib/filterx/object-json-object.c
index 0ae14dc64..e80f10bec 100644
--- a/lib/filterx/object-json-object.c
+++ b/lib/filterx/object-json-object.c
@@ -245,7 +245,6 @@ filterx_json_object_new_sub(struct json_object *jso, FilterXObject *root)
   FilterXJsonObject *self = g_new0(FilterXJsonObject, 1);
   filterx_dict_init_instance(&self->super, &FILTERX_TYPE_NAME(json_object));
 
-  self->super.super.make_readonly = _make_readonly;
   self->super.get_subscript = _get_subscript;
   self->super.set_subscript = _set_subscript;
   self->super.unset_key = _unset_key;
@@ -320,4 +319,5 @@ FILTERX_DEFINE_TYPE(json_object, FILTERX_TYPE_NAME(dict),
                     .clone = _clone,
                     .list_factory = filterx_json_array_new_empty,
                     .dict_factory = filterx_json_object_new_empty,
+                    .make_readonly = _make_readonly,
                    );