diff --git a/src/Guzzle/Service/Command/LocationVisitor/Request/JsonVisitor.php b/src/Guzzle/Service/Command/LocationVisitor/Request/JsonVisitor.php
index 47c32f25..c34c5cae 100644
--- a/src/Guzzle/Service/Command/LocationVisitor/Request/JsonVisitor.php
+++ b/src/Guzzle/Service/Command/LocationVisitor/Request/JsonVisitor.php
@@ -14,7 +14,7 @@ class JsonVisitor extends AbstractRequestVisitor
     /**
      * @var bool Whether or not to add a Content-Type header when JSON is found
      */
-    protected $jsonContentType = null;
+    protected $jsonContentType = 'application/json';
 
     /**
      * @var \SplObjectStorage Data object for persisting JSON data