diff --git a/src/display/api.js b/src/display/api.js
index 8fd0dfa94..2df8f358a 100644
--- a/src/display/api.js
+++ b/src/display/api.js
@@ -1519,6 +1519,7 @@ var PDFWorker = (function PDFWorkerClosure() {
         this._webWorker.terminate();
         this._webWorker = null;
       }
+      pdfWorkerPorts.delete(this._port);
       this._port = null;
       if (this._messageHandler) {
         this._messageHandler.destroy();