diff --git a/doc/TODO b/doc/TODO
index 6874727794..7b45b3d2e1 100644
--- a/doc/TODO
+++ b/doc/TODO
@@ -53,6 +53,8 @@ N  - Make millisecond accuracy work on win32
 Tier two:
 
    - Handle pools of waiting circuits better.
+   - Limit number of circuits that we preemptively generate based on past
+     behavior; use same limits in circuit_expire_old_circuits().
    - Let more config options (e.g. ORPort) change dynamically.
    - Write limiting; configurable token buckets.
    - Only the top of a directory needs to be signed.