diff --git a/lib/transports/websocket.js b/lib/transports/websocket.js
index 1daf6caa9..fdaeffb6c 100644
--- a/lib/transports/websocket.js
+++ b/lib/transports/websocket.js
@@ -79,7 +79,7 @@ class WebSocket extends Transport {
     const send = data => {
       if (this.perMessageDeflate) {
         const len =
-          "string" === typeof data ? Buffer.byteLength(data) : data.length;
+          "string" === typeof data ? data.length : Buffer.byteLength(data);
         if (len < this.perMessageDeflate.threshold) {
           opts.compress = false;
         }