diff --git a/gtk/gtktreemodel.c b/gtk/gtktreemodel.c
index 526d168..7eb9355 100644
--- a/gtk/gtktreemodel.c
+++ b/gtk/gtktreemodel.c
@@ -1094,7 +1094,7 @@ gtk_tree_model_get_string_from_iter (GtkTreeModel *tree_model,
 /**
  * gtk_tree_model_get_iter_first:
  * @tree_model: A #GtkTreeModel.
- * @iter: The uninitialized #GtkTreeIter.
+ * @iter: (out caller-allocates): The uninitialized #GtkTreeIter.
  * 
  * Initializes @iter with the first iterator in the tree (the one at the path
  * "0") and returns %TRUE.  Returns %FALSE if the tree is empty.
