diff --git a/api.planx.uk/server.ts b/api.planx.uk/server.ts
index 78af294e10..ee394f463b 100644
--- a/api.planx.uk/server.ts
+++ b/api.planx.uk/server.ts
@@ -52,7 +52,7 @@ const checkAllowedOrigins: CorsOptions["origin"] = (origin, callback) => {
 
   isTest || isDevelopment || isAllowed || isMapDocs
     ? callback(null, true)
-    : callback(new Error("Not allowed by CORS"));
+    : callback(new Error(`Not allowed by CORS. Origin: ${origin}`));
 };
 
 app.use(