diff --git a/CHANGELOG.md b/CHANGELOG.md
index ac8eabe5..6c141f41 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,8 @@
 # Changelog
 
-## next
+## [v0.20.0](https://github.com/chimurai/http-proxy-middleware/releases/tag/v0.20.0)
 
+- fix(ws): concurrent websocket requests do not get upgraded ([#335](https://github.com/chimurai/http-proxy-middleware/issues/335))
 - chore: drop node 6 (BREAKING CHANGE)
 - chore: update to micromatch@4 ([BREAKING CHANGE](https://github.com/micromatch/micromatch/blob/master/CHANGELOG.md#400---2019-03-20))
 - chore: update dev dependencies
diff --git a/examples/websocket/index.html b/examples/websocket/index.html
index 27519122..62ab2ecf 100644
--- a/examples/websocket/index.html
+++ b/examples/websocket/index.html
@@ -67,11 +67,13 @@ <h2>WebSocket demo</h2>
 
         function connect() {
           setupSocket(location.value);
+          toggleControls();
         }
 
         function disconnect() {
           socket.close();
           socket = undefined;
+          toggleControls();
         }
 
         function sendMessage(val) {
@@ -83,11 +85,9 @@ <h2>WebSocket demo</h2>
           socket = new WebSocket(url);
           socket.addEventListener('open', () => {
             log('CONNECTED');
-            toggleControls();
           })
           socket.addEventListener('close', () => {
             log('DISCONNECTED');
-            toggleControls()
           })
           socket.addEventListener('error', () => { log('SOCKET ERROR OCCURED'); })
           socket.addEventListener('message', (msg) => { log('RECEIVED:' + msg.data); })
diff --git a/package.json b/package.json
index 2c96dfbc..e5a9b251 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "http-proxy-middleware",
-  "version": "0.20.0-beta.2",
+  "version": "0.20.0",
   "description": "The one-liner node.js proxy middleware for connect, express and browser-sync",
   "main": "dist/index.js",
   "files": [
diff --git a/src/http-proxy-middleware.ts b/src/http-proxy-middleware.ts
index e1a0d6fe..342e9da2 100644
--- a/src/http-proxy-middleware.ts
+++ b/src/http-proxy-middleware.ts
@@ -60,10 +60,12 @@ export class HttpProxyMiddleware {
   };
 
   private catchUpgradeRequest = server => {
-    server.on('upgrade', this.handleUpgrade);
-    // prevent duplicate upgrade handling;
-    // in case external upgrade is also configured
-    this.wsInternalSubscribed = true;
+    if (!this.wsInternalSubscribed) {
+      server.on('upgrade', this.handleUpgrade);
+      // prevent duplicate upgrade handling;
+      // in case external upgrade is also configured
+      this.wsInternalSubscribed = true;
+    }
   };
 
   private handleUpgrade = (req, socket, head) => {