diff --git a/core/lib/Drupal/Component/Utility/UrlHelper.php b/core/lib/Drupal/Component/Utility/UrlHelper.php
index 691413e..b74a8d1 100644
--- a/core/lib/Drupal/Component/Utility/UrlHelper.php
+++ b/core/lib/Drupal/Component/Utility/UrlHelper.php
@@ -51,7 +51,7 @@ public static function buildQuery(array $query, $parent = '') {
     $params = array();
 
     foreach ($query as $key => $value) {
-      $key = ($parent ? $parent . '[' . rawurlencode($key) . ']' : rawurlencode($key));
+      $key = ($parent ? $parent . rawurlencode('[' . $key . ']') : rawurlencode($key));
 
       // Recurse into children.
       if (is_array($value)) {
diff --git a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
index 0477b7a..09b4be2 100644
--- a/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
+++ b/core/tests/Drupal/Tests/Component/Utility/UrlHelperTest.php
@@ -28,7 +28,7 @@ public function providerTestBuildQuery() {
       array(array('a' => ' &#//+%20@۞'), 'a=%20%26%23//%2B%2520%40%DB%9E', 'Value was properly encoded.'),
       array(array(' &#//+%20@۞' => 'a'), '%20%26%23%2F%2F%2B%2520%40%DB%9E=a', 'Key was properly encoded.'),
       array(array('a' => '1', 'b' => '2', 'c' => '3'), 'a=1&b=2&c=3', 'Multiple values were properly concatenated.'),
-      array(array('a' => array('b' => '2', 'c' => '3'), 'd' => 'foo'), 'a[b]=2&a[c]=3&d=foo', 'Nested array was properly encoded.'),
+      array(array('a' => array('b' => '2', 'c' => '3'), 'd' => 'foo'), 'a%5Bb%5D=2&a%5Bc%5D=3&d=foo', 'Nested array was properly encoded.'),
       array(array('foo' => NULL), 'foo', 'Simple parameters are properly added.'),
     );
   }