diff --git a/src/Symfony/Component/HttpFoundation/Request.php b/src/Symfony/Component/HttpFoundation/Request.php
index eb4bdb6481..18b10101c4 100644
--- a/src/Symfony/Component/HttpFoundation/Request.php
+++ b/src/Symfony/Component/HttpFoundation/Request.php
@@ -406,9 +406,8 @@ class Request
         $dup->method = null;
         $dup->format = null;
 
-        if (!$dup->get('_format')) {
-            // we set the request format to null if the current request is not known
-            $dup->setRequestFormat($this->getRequestFormat(null));
+        if (!$dup->get('_format') && $this->get('_format')) {
+            $dup->attributes->set('_format', $this->get('_format'));
         }
 
         return $dup;
diff --git a/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php b/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
index bd06b85cfa..6bbaff9297 100644
--- a/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
+++ b/src/Symfony/Component/HttpFoundation/Tests/RequestTest.php
@@ -259,9 +259,6 @@ class RequestTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals('foo=bar', $request->getQueryString());
     }
 
-    /**
-     * @covers Symfony\Component\HttpFoundation\Request::duplicate
-     */
     public function testDuplicate()
     {
         $request = new Request(array('foo' => 'bar'), array('foo' => 'bar'), array('foo' => 'bar'), array(), array(), array('HTTP_FOO' => 'bar'));
@@ -280,6 +277,15 @@ class RequestTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals(array('foo' => array('foobar')), $dup->headers->all(), '->duplicate() overrides the HTTP header if provided');
     }
 
+    public function testDuplicateWithFormat()
+    {
+        $request = new Request(array(), array(), array('_format' => 'json'));
+        $dup = $request->duplicate();
+
+        $this->assertEquals('json', $dup->getRequestFormat());
+        $this->assertEquals('json', $dup->attributes->get('_format'));
+    }
+
     /**
      * @covers Symfony\Component\HttpFoundation\Request::getFormat
      * @covers Symfony\Component\HttpFoundation\Request::setFormat