diff --git a/static/protocol.js b/static/protocol.js
index 65e2fc5..e1864f4 100644
--- a/static/protocol.js
+++ b/static/protocol.js
@@ -783,8 +783,10 @@ ServerConnection.prototype.gotRenegotiate = function(id) {
  */
 ServerConnection.prototype.gotClose = function(id) {
     let c = this.down[id];
-    if(!c)
+    if(!c) {
         console.warn('unknown down stream', id);
+        return;
+    }
     c.close();
 };