diff --git a/utils/receiver.php b/utils/receiver.php
index d3b2177..7c9ac6c 100644
--- a/utils/receiver.php
+++ b/utils/receiver.php
@@ -98,7 +98,7 @@ public function getAuthor($webmention)
         ];
     }
 
-    private function isKnownNetwork(string $authorUrl): boolean
+    private function isKnownNetwork(string $authorUrl)
     {
         $networkHosts = [
             'twitter.com',