diff --git a/src/Server/Transport/StreamableHttpTransport.php b/src/Server/Transport/StreamableHttpTransport.php
index 2b1e6869..d93110e9 100644
--- a/src/Server/Transport/StreamableHttpTransport.php
+++ b/src/Server/Transport/StreamableHttpTransport.php
@@ -242,6 +242,10 @@ protected function createErrorResponse(Error $jsonRpcError, int $statusCode): Re
             ->withHeader('Content-Type', 'application/json')
             ->withBody($this->streamFactory->createStream($payload));
 
+        if ($statusCode === 405) {
+            $response = $response->withHeader('Allow', 'POST, DELETE, OPTIONS');
+        }
+
         return $this->withCorsHeaders($response);
     }