diff --git a/lib/matplotlib/backends/web_backend/js/nbagg_mpl.js b/lib/matplotlib/backends/web_backend/js/nbagg_mpl.js
index 7a9544973957..8e7e38157925 100644
--- a/lib/matplotlib/backends/web_backend/js/nbagg_mpl.js
+++ b/lib/matplotlib/backends/web_backend/js/nbagg_mpl.js
@@ -7,6 +7,17 @@ var comm_websocket_adapter = function (comm) {
     var ws = {};
 
     ws.binaryType = comm.kernel.ws.binaryType;
+    ws.readyState = comm.kernel.ws.readyState;
+    function updateReadyState(_event) {
+        if (comm.kernel.ws) {
+            ws.readyState = comm.kernel.ws.readyState;
+        } else {
+            ws.readyState = 3; // Closed state.
+        }
+    }
+    comm.kernel.ws.addEventListener('open', updateReadyState);
+    comm.kernel.ws.addEventListener('close', updateReadyState);
+    comm.kernel.ws.addEventListener('error', updateReadyState);
 
     ws.close = function () {
         comm.close();