diff --git a/core/modules/rest/lib/Drupal/rest/Plugin/views/display/RestExport.php b/core/modules/rest/lib/Drupal/rest/Plugin/views/display/RestExport.php
index 5ce4a52..a32e0e1 100644
--- a/core/modules/rest/lib/Drupal/rest/Plugin/views/display/RestExport.php
+++ b/core/modules/rest/lib/Drupal/rest/Plugin/views/display/RestExport.php
@@ -59,7 +59,7 @@ class RestExport extends PathPluginBase {
    *
    * @var string
    */
-  protected $contentType;
+  protected $contentType = 'json';
 
   /**
    * The mime type for the response.
@@ -78,7 +78,12 @@ public function initDisplay(ViewExecutable $view, array &$display, array &$optio
     $negotiation = $container->get('content_negotiation');
     $request = $container->get('request');
 
-    $this->setContentType($negotiation->getContentType($request));
+    $request_content_type = $negotiation->getContentType($request);
+    // Only set the requested content type if it's not html.
+    if ($request_content_type !== 'html') {
+      $this->setContentType($request_content_type);
+    }
+
     $this->setMimeType($request->getMimeType($this->contentType));
   }
 
diff --git a/core/modules/rest/lib/Drupal/rest/Tests/Views/StyleSerializerTest.php b/core/modules/rest/lib/Drupal/rest/Tests/Views/StyleSerializerTest.php
index 5349955..be89aa9 100644
--- a/core/modules/rest/lib/Drupal/rest/Tests/Views/StyleSerializerTest.php
+++ b/core/modules/rest/lib/Drupal/rest/Tests/Views/StyleSerializerTest.php
@@ -126,6 +126,11 @@ public function testSerializerResponses() {
     $expected = $serializer->serialize($entities, 'hal_json');
     $actual_json = $this->drupalGet('test/serialize/entity', array(), array('Accept: application/hal+json'));
     $this->assertIdentical($actual_json, $expected, 'The expected HAL output was found.');
+
+    // Test that by default the output will be JSON.
+    $expected = $serializer->serialize($entities, 'json');
+    $actual_xml = $this->drupalGet('test/serialize/entity');
+    $this->assertIdentical($actual_xml, $expected, 'By default json output is returned.');
   }
 
   /**