diff --git a/appengine/analytics/app.js b/appengine/analytics/app.js
index 8a1701b466..2194d9b6e6 100644
--- a/appengine/analytics/app.js
+++ b/appengine/analytics/app.js
@@ -26,7 +26,7 @@ app.enable('trust proxy');
 // Engine, but will need to be set manually when running locally. See README.md.
 const GA_TRACKING_ID = process.env.GA_TRACKING_ID;
 
-function trackEvent (category, action, label, value, cb) {
+function trackEvent (category, action, label, value) {
   const data = {
     // API Version.
     v: '1',