diff --git a/ChangeLog b/ChangeLog
index 3dc25f99e8..a788ecaee1 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,4 +1,9 @@
 Changes in version 0.2.1.1-alpha - 2008-??-??
+  o Major bugfixes:
+    - Fix assertion failure that could occur when a blocked circuit became
+      unblocked, and it had pending client DNS requests.  Bugfix on
+      0.2.0.1-alpha.  Fixes bug 632.
+
   o Minor bugfixes:
     - Stop giving double-close warn when we reject an address for client DNS.
     - On Windows, correctly detect errors when listing the contents of a
diff --git a/src/or/relay.c b/src/or/relay.c
index 0d863cd972..db7d1a3d77 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -1813,6 +1813,12 @@ set_streams_blocked_on_circ(circuit_t *circ, or_connection_t *orconn,
     connection_t *conn = TO_CONN(edge);
     conn->edge_blocked_on_circ = block;
 
+    if (!conn->read_event) {
+      /* This connection is a placeholder for something; probably a DNS
+       * request.  It can't actually stop or start reading.*/
+      continue;
+    }
+
     if (block) {
       if (connection_is_reading(conn))
         connection_stop_reading(conn);