diff --git a/public/scripts/cookie.js b/public/scripts/cookie.js
index a99a6e3dca93c..200e9dc74350a 100644
--- a/public/scripts/cookie.js
+++ b/public/scripts/cookie.js
@@ -57,7 +57,7 @@ const toISOFormat = (date) => {
 
 const shouldOverwrite = (new_utm_data, current_utm_data) => {
   // If we don't have old utm data, the utm_source field is enough for new utm data
-  if (!current_utm_data && new_utm_data.utm_source !== undefined) {
+  if (!current_utm_data && new_utm_data.utm_source !== "null") {
     return true;
   }