diff --git a/app/controllers/admin/loginstyle.php b/app/controllers/admin/loginstyle.php
index ddcae296572dfc67f5d20f161bd87aac74e85e06..f998b3a6a6677b648a92f1bd8a3e88844e2f3291 100644
--- a/app/controllers/admin/loginstyle.php
+++ b/app/controllers/admin/loginstyle.php
@@ -60,6 +60,7 @@ class Admin_LoginStyleController extends AuthenticatedController
             }
 
             $extension = pathinfo($filename, PATHINFO_EXTENSION);
+            $extension = strtolower($extension);
             if (!in_array($extension, ['gif', 'jpeg', 'jpg', 'png'])) {
                 continue;
             }