diff --git a/lib/routes.js b/lib/routes.js
index 0009c25..4fd1766 100644
--- a/lib/routes.js
+++ b/lib/routes.js
@@ -84,6 +84,9 @@ const setupRoutes = function setupRoutes() {
       };
 
       socket.progress = (data) => {
+        if (socket.readyState !== 1) {
+          return;
+        }
         socket.send(prep({ action: 'progress', data }));
       };