diff --git a/web/viewer.js b/web/viewer.js
index 44f20ecc2..15ef9ca0e 100644
--- a/web/viewer.js
+++ b/web/viewer.js
@@ -15,6 +15,13 @@
 
 "use strict";
 
+/* eslint-disable-next-line no-unused-vars */
+const pdfjsVersion =
+  typeof PDFJSDev !== "undefined" ? PDFJSDev.eval("BUNDLE_VERSION") : void 0;
+/* eslint-disable-next-line no-unused-vars */
+const pdfjsBuild =
+  typeof PDFJSDev !== "undefined" ? PDFJSDev.eval("BUNDLE_BUILD") : void 0;
+
 if (typeof PDFJSDev !== "undefined" && PDFJSDev.test("CHROME")) {
   var defaultUrl; // eslint-disable-line no-var