diff --git a/src/or/circuituse.c b/src/or/circuituse.c
index e9c20f59a8..22b9916818 100644
--- a/src/or/circuituse.c
+++ b/src/or/circuituse.c
@@ -991,9 +991,7 @@ connection_ap_handshake_attach_chosen_circuit(connection_t *conn,
              conn->state == AP_CONN_STATE_CONTROLLER_WAIT);
   tor_assert(conn->socks_request);
   tor_assert(circ);
-
-  if (circ->state != CIRCUIT_STATE_OPEN)
-    return 0;
+  tor_assert(circ->state == CIRCUIT_STATE_OPEN);
 
   conn->state = AP_CONN_STATE_CIRCUIT_WAIT;
 
diff --git a/src/or/control.c b/src/or/control.c
index 28940e1d4d..47c0cc0e68 100644
--- a/src/or/control.c
+++ b/src/or/control.c
@@ -745,6 +745,10 @@ static int handle_control_attachstream(connection_t *conn, uint32_t len,
     send_control_error(conn, ERR_NO_CIRC, "No circuit found with given ID");
     return 0;
   }
+  if (circ->state != CIRCUIT_STATE_OPEN) {
+    send_control_error(conn, ERR_INTERNAL, "Refuse to attach stream to non-open circ.");
+    return 0;
+  }
   if (connection_ap_handshake_attach_chosen_circuit(ap_conn, circ) != 1) {
     send_control_error(conn, ERR_INTERNAL, "Unable to attach stream.");
     return 0;