diff --git a/gio/gactiongroup.c b/gio/gactiongroup.c
index 1faaf6d07..b41173787 100644
--- a/gio/gactiongroup.c
+++ b/gio/gactiongroup.c
@@ -734,10 +734,10 @@ g_action_group_action_state_changed (GActionGroup *action_group,
  * @action_group: a [type@Gio.ActionGroup]
  * @action_name: the name of an action in the group
  * @enabled: (out): if the action is presently enabled
- * @parameter_type: (out) (transfer none) (optional): the parameter type, or `NULL` if none needed
- * @state_type: (out) (transfer none) (optional): the state type, or `NULL` if stateless
- * @state_hint: (out) (optional): the state hint, or `NULL` if none
- * @state: (out) (optional): the current state, or `NULL` if stateless
+ * @parameter_type: (out) (transfer none) (optional) (nullable): the parameter type, or `NULL` if none needed
+ * @state_type: (out) (transfer none) (optional) (nullable): the state type, or `NULL` if stateless
+ * @state_hint: (out) (optional) (nullable): the state hint, or `NULL` if none
+ * @state: (out) (optional) (nullable): the current state, or `NULL` if stateless
  *
  * Queries all aspects of the named action within an @action_group.
  *