diff --git a/lib/behaviours/session_store.ex b/lib/behaviours/session_store.ex
index 14eb64f..b9faded 100644
--- a/lib/behaviours/session_store.ex
+++ b/lib/behaviours/session_store.ex
@@ -21,4 +21,5 @@ defmodule Behaviours.SessionStore do
               {:ok, String.t()} | :error
 
   @callback session_ids_for_user(user_id :: String.t()) :: list()
+  @callback max_ttl(user_id :: String.t()) :: String.t() | nil
 end