diff --git a/app/Http/Controllers/Client/ClientController.php b/app/Http/Controllers/Client/ClientController.php
index 17d48e76..fa34145a 100644
--- a/app/Http/Controllers/Client/ClientController.php
+++ b/app/Http/Controllers/Client/ClientController.php
@@ -124,7 +124,7 @@ class ClientController extends Controller
 
         // Subscription link
         $subsURL = 'http';
-        if ($_SERVER['HTTPS'] == 'on') {
+        if (isset( $_SERVER['HTTPS'] ) && strtolower( $_SERVER['HTTPS'] ) == 'on') {
             $subsURL .= 's';
         }
         $subsURL .= '://';