diff --git a/lib/API/JSON/v1/Newsletters.php b/lib/API/JSON/v1/Newsletters.php
index b9bf43c33f..c31835c932 100644
--- a/lib/API/JSON/v1/Newsletters.php
+++ b/lib/API/JSON/v1/Newsletters.php
@@ -267,6 +267,8 @@ class Newsletters extends APIEndpoint {
         $newsletter,
         $subscriber
       );
+      // strip protocol to avoid mix content error
+      $preview_url = preg_replace('{^https?:}i', '', $preview_url);
 
       return $this->successResponse(
         Newsletter::findOne($newsletter->id)->asArray(),
diff --git a/tests/unit/API/JSON/v1/NewslettersTest.php b/tests/unit/API/JSON/v1/NewslettersTest.php
index 98b4a1eab2..70a65a3825 100644
--- a/tests/unit/API/JSON/v1/NewslettersTest.php
+++ b/tests/unit/API/JSON/v1/NewslettersTest.php
@@ -1,12 +1,13 @@
 <?php
+
 namespace MailPoet\Test\API\JSON\v1;
 
 use Carbon\Carbon;
 use Codeception\Util\Fixtures;
 use Codeception\Util\Stub;
 use Helper\WordPressHooks as WPHooksHelper;
-use MailPoet\API\JSON\v1\Newsletters;
 use MailPoet\API\JSON\Response as APIResponse;
+use MailPoet\API\JSON\v1\Newsletters;
 use MailPoet\Models\Newsletter;
 use MailPoet\Models\NewsletterOption;
 use MailPoet\Models\NewsletterOptionField;
@@ -747,6 +748,17 @@ class NewslettersTest extends \MailPoetTest {
     expect($response->errors[0]['message'])->equals('The email could not be sent: failed');
   }
 
+  function testItReturnsBrowserPreviewUrlWithoutProtocol() {
+    $data = array(
+      'id' => $this->newsletter->id,
+      'body' => 'fake body'
+    );
+    $router = new Newsletters();
+    $response = $router->showPreview($data);
+    expect($response->meta['preview_url'])->notContains('http');
+    expect($response->meta['preview_url'])->regExp('!^\/\/!');
+  }
+
   function testItGeneratesPreviewLinksWithNewsletterHashAndNoSubscriberData() {
     $router = new Newsletters();
     $response = $router->listing();
@@ -767,4 +779,4 @@ class NewslettersTest extends \MailPoetTest {
     \ORM::raw_execute('TRUNCATE ' . Segment::$_table);
     \ORM::raw_execute('TRUNCATE ' . SendingQueue::$_table);
   }
-}
+}
\ No newline at end of file