diff --git a/doc/TODO b/doc/TODO
index 9700eaa311..5e9fdee16f 100644
--- a/doc/TODO
+++ b/doc/TODO
@@ -57,7 +57,7 @@ N . Additional controller features
 
   . Helper nodes
     . More testing and debugging
-    - On sighup, if usehelpernodes changed to 1, use new circuits?
+    o On sighup, if usehelpernodes changed to 1, use new circuits?
     - If your helper nodes are unavailable, don't abandon them unless
       other nodes *are* reachable.
 R   - If you think an OR conn is open but you can never establish a circuit
diff --git a/src/or/config.c b/src/or/config.c
index 4655e2c2bd..d7ac5f72c6 100644
--- a/src/or/config.c
+++ b/src/or/config.c
@@ -623,6 +623,12 @@ options_act(or_options_t *old_options)
 
   /* Check for transitions that need action. */
   if (old_options) {
+    if (options->UseHelperNodes && !old_options->UseHelperNodes) {
+      log_fn(LOG_INFO, "Switching to helper nodes; abandoning previous circuits");
+      circuit_mark_all_unused_circs();
+      circuit_expire_all_dirty_circs();
+    }
+
     if (options_transition_affects_workers(old_options, options)) {
       log_fn(LOG_INFO,"Worker-related options changed. Rotating workers.");
       cpuworkers_rotate();