diff --git a/core/rfb.js b/core/rfb.js
index 2257da3c..074eb519 100644
--- a/core/rfb.js
+++ b/core/rfb.js
@@ -484,6 +484,10 @@ export default class RFB extends EventTargetMixin {
             if (this._sock.readyState === 'closed') {
                 this._fail("Cannot use already closed WebSocket/RTCDataChannel");
             }
+
+            if (this._sock.readyState === 'open') {
+                this._socketOpen();
+            }
         }
 
         // Make our elements part of the page
diff --git a/core/websock.js b/core/websock.js
index 52e27be5..37b33fcc 100644
--- a/core/websock.js
+++ b/core/websock.js
@@ -247,7 +247,7 @@ export default class Websock {
         this._websocket.binaryType = "arraybuffer";
         this._websocket.onmessage = this._recvMessage.bind(this);
 
-        const onOpen = () => {
+        this._websocket.onopen = () => {
             Log.Debug('>> WebSock.onopen');
             if (this._websocket.protocol) {
                 Log.Info("Server choose sub-protocol: " + this._websocket.protocol);
@@ -257,12 +257,6 @@ export default class Websock {
             Log.Debug("<< WebSock.onopen");
         };
 
-        if (this.readyState === 'open') {
-            onOpen();
-        } else {
-            this._websocket.onopen = onOpen;
-        }
-
         this._websocket.onclose = (e) => {
             Log.Debug(">> WebSock.onclose");
             this._eventHandlers.close(e);
diff --git a/tests/test.rfb.js b/tests/test.rfb.js
index 2c112f3a..c99edc75 100644
--- a/tests/test.rfb.js
+++ b/tests/test.rfb.js
@@ -183,6 +183,20 @@ describe('Remote Frame Buffer Protocol Client', function () {
                 expect(attach).to.have.been.calledOnceWithExactly(sock);
             });
 
+            it('should handle already open WebSocket/RTCDataChannel objects', function () {
+                let sock = new FakeWebSocket('ws://HOST:8675/PATH', []);
+                sock._open();
+                const client = new RFB(document.createElement('div'), sock);
+                let callback = sinon.spy();
+                client.addEventListener('disconnect', callback);
+                this.clock.tick();
+                expect(open).to.not.have.been.called;
+                expect(attach).to.have.been.calledOnceWithExactly(sock);
+                // Check if it is ready for some data
+                sock._receiveData(new Uint8Array(['R', 'F', 'B', '0', '0', '3', '0', '0', '8']));
+                expect(callback).to.not.have.been.called;
+            });
+
             it('should refuse closed WebSocket/RTCDataChannel objects', function () {
                 let sock = new FakeWebSocket('ws://HOST:8675/PATH', []);
                 sock.readyState = WebSocket.CLOSED;
diff --git a/tests/test.websock.js b/tests/test.websock.js
index 1c2aa13c..857fdca8 100644
--- a/tests/test.websock.js
+++ b/tests/test.websock.js
@@ -271,23 +271,10 @@ describe('Websock', function () {
         });
 
         describe('attaching', function () {
-            it('should attach to an existing open websocket', function () {
+            it('should attach to an existing websocket', function () {
                 let ws = new FakeWebSocket('ws://localhost:8675');
-                ws._open();
-                let callback = sinon.spy();
-                sock.on('open', callback);
                 sock.attach(ws);
                 expect(WebSocket).to.not.have.been.called;
-                expect(callback).to.have.been.calledOnce;
-            });
-
-            it('should attach to an existing connecting websocket', function () {
-                let ws = new FakeWebSocket('ws://localhost:8675');
-                let callback = sinon.spy();
-                sock.on('open', callback);
-                sock.attach(ws);
-                expect(WebSocket).to.not.have.been.called;
-                expect(callback).to.not.have.been.called;
             });
         });