diff --git a/src/Formatter/FormatPostMentions.php b/src/Formatter/FormatPostMentions.php
index d4b47b8..c1a002f 100644
--- a/src/Formatter/FormatPostMentions.php
+++ b/src/Formatter/FormatPostMentions.php
@@ -24,7 +24,7 @@ class FormatPostMentions
      * @param Psr\Http\Message\ServerRequestInterface $request
      * @return void
      */
-    public function __invoke(Renderer $renderer, $context, $xml, Request $request)
+    public function __invoke(Renderer $renderer, $context, $xml, Request $request = null)
     {
         $post = $context;
 
diff --git a/src/Formatter/FormatUserMentions.php b/src/Formatter/FormatUserMentions.php
index 7d160aa..d97a2b8 100644
--- a/src/Formatter/FormatUserMentions.php
+++ b/src/Formatter/FormatUserMentions.php
@@ -23,7 +23,7 @@ class FormatUserMentions
      * @param string|null $xml
      * @param Psr\Http\Message\ServerRequestInterface $request
      */
-    public function __invoke(Renderer $renderer, $context, $xml, Request $request)
+    public function __invoke(Renderer $renderer, $context, $xml, Request $request = null)
     {
         $post = $context;