diff --git a/lib/sender.js b/lib/sender.js
index 75c78fb35..d385d6456 100644
--- a/lib/sender.js
+++ b/lib/sender.js
@@ -318,6 +318,7 @@ class Sender {
 
     const perMessageDeflate = this._extensions[PerMessageDeflate.extensionName];
 
+    this._bufferedBytes += data.length;
     this._deflating = true;
     perMessageDeflate.compress(data, options.fin, (_, buf) => {
       if (this._socket.destroyed) {
@@ -336,6 +337,7 @@ class Sender {
         return;
       }
 
+      this._bufferedBytes -= data.length;
       this._deflating = false;
       options.readOnly = false;
       this.sendFrame(Sender.frame(buf, options), cb);
diff --git a/test/websocket.test.js b/test/websocket.test.js
index ef3746028..64d52bec9 100644
--- a/test/websocket.test.js
+++ b/test/websocket.test.js
@@ -185,13 +185,16 @@ describe('WebSocket', () => {
 
             ws.on('open', () => {
               ws.send('foo');
+
+              assert.strictEqual(ws.bufferedAmount, 3);
+
               ws.send('bar', (err) => {
                 assert.ifError(err);
                 assert.strictEqual(ws.bufferedAmount, 0);
                 wss.close(done);
               });
 
-              assert.strictEqual(ws.bufferedAmount, 3);
+              assert.strictEqual(ws.bufferedAmount, 6);
             });
           }
         );