diff --git a/src/Controller/Services.php b/src/Controller/Services.php
index 0af4095..d0ef0c6 100644
--- a/src/Controller/Services.php
+++ b/src/Controller/Services.php
@@ -76,7 +76,7 @@ class Services extends ControllerBase {
     }
     // Find the request format to determin how we're going to serialize this
     // data.
-    $format = $request->getRequestFormat();
+    $format = $request->get('_format', 'html');
     $data = $this->serializer->serialize($data, $format);
     /*
      * Create a new Cacheable Response object with our serialized data, set its