diff --git a/treetrie.h b/treetrie.h
index dd92abd..d7feb89 100644
--- a/treetrie.h
+++ b/treetrie.h
@@ -83,8 +83,7 @@ extern void tt_dump_arena(tt_arena_t *a);
 
 extern void tt_arena_flush(tt_arena_t *a);
 
-/* Returns 0 if consing failed (because of out-of-memory).
-   Otherwise, returns a nonzero index.
+/* Returns TT_NO_PTR if consing failed (because of out-of-memory).
    Grabs na and nb (according to tag) IF it needs to allocate a new node, otherwise does not.
    DOES NOT increase the reference count of the returned node. */
 extern tt_node_ptr_t tt_arena_cons(tt_arena_t *a,