diff --git a/src/MultipartStreamBuilder.php b/src/MultipartStreamBuilder.php
index 0efb760..f09b308 100644
--- a/src/MultipartStreamBuilder.php
+++ b/src/MultipartStreamBuilder.php
@@ -91,9 +91,9 @@ public function addData($resource, array $headers = [])
     /**
      * Add a resource to the Multipart Stream.
      *
-     * @param string                                                      $name     the formpost name
-     * @param string|resource|StreamInterface                             $resource
-     * @param array{'headers': array<string, string>, 'filename': string} $options
+     * @param string                                                        $name     the formpost name
+     * @param string|resource|StreamInterface                               $resource
+     * @param array{'headers?': array<string, string>, 'filename?': string} $options
      *
      * Options:
      * - headers: additional headers as hashmap ['header-name' => 'header-value']