diff --git a/src/Symfony/Component/Mime/Header/Headers.php b/src/Symfony/Component/Mime/Header/Headers.php
index f60cd474a6..c0e45e0d0a 100644
--- a/src/Symfony/Component/Mime/Header/Headers.php
+++ b/src/Symfony/Component/Mime/Header/Headers.php
@@ -168,7 +168,7 @@ final class Headers
     public function get(string $name): ?HeaderInterface
     {
         $name = strtolower($name);
-        if (!isset($this->headers[strtolower($name)])) {
+        if (!isset($this->headers[$name])) {
             return null;
         }