diff --git a/src/Requests/ServerRequest.php b/src/Requests/ServerRequest.php
index c11d07e..abe87aa 100644
--- a/src/Requests/ServerRequest.php
+++ b/src/Requests/ServerRequest.php
@@ -58,7 +58,7 @@ public function extractHeadersFromServer(): array
         $headers = [];
         foreach ($_SERVER as $name => $value) {
             if (0 === stripos($name, 'HTTP_')) {
-                $key = substr($name, 5);
+                $key = strtolower(substr($name, 5));
                 $headers[$key] = [$value];
             }
         }