core/authorize.php                                        |  2 +-
 core/includes/batch.inc                                   |  4 ++--
 core/includes/errors.inc                                  |  4 ++--
 core/includes/install.core.inc                            |  4 ++--
 .../Core/EventSubscriber/HtmlResponseSubscriber.php       | 15 +++++++++------
 core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php      |  4 ++--
 6 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/core/authorize.php b/core/authorize.php
index 4d9df40..a3d33c7 100644
--- a/core/authorize.php
+++ b/core/authorize.php
@@ -166,7 +166,7 @@ function authorize_access_allowed(Request $request) {
     '#show_messages' => $show_messages,
   )));
 
-  // Prepare attachments, because this does not go the usual way via the
+  // Process attachments, because this does not go the usual way via the
   // Symfony chain, but is sent directly.
   $bare_html_page_renderer->prepareAttachments($response);
 
diff --git a/core/includes/batch.inc b/core/includes/batch.inc
index 8ac05b8..f7d6870 100644
--- a/core/includes/batch.inc
+++ b/core/includes/batch.inc
@@ -146,9 +146,9 @@ function _batch_progress_page() {
     // Use a HtmlResponse to process the attachments.
     $response = new HtmlResponse($content);
 
-    // Prepare attachments, because this does not go the usual way via the
+    // Process attachments, because this does not go the usual way via the
     // Symfony chain, but is sent directly.
-    $bare_html_page_renderer->prepareAttachments($response);
+    $bare_html_page_renderer->processAttachments($response);
 
     // Just use the content of the response.
     $fallback = $response->getContent();
diff --git a/core/includes/errors.inc b/core/includes/errors.inc
index 8ed39b6..c1c3664 100644
--- a/core/includes/errors.inc
+++ b/core/includes/errors.inc
@@ -248,9 +248,9 @@ function _drupal_log_error($error, $fatal = FALSE) {
       $output = $bare_html_page_renderer->renderBarePage(['#markup' => $message], 'Error', 'maintenance_page');
 
       $response = new HtmlResponse($output, 500);
-      // Prepare attachments, because this does not go the usual way via the
+      // Process attachments, because this does not go the usual way via the
       // Symfony chain, but is sent directly.
-      $bare_html_page_renderer->prepareAttachments($response);
+      $bare_html_page_renderer->processAttachments($response);
 
       $response->setStatusCode(500, '500 Service unavailable (with message)');
       // An exception must halt script execution.
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index 9f277b0..4ea52cc 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -996,9 +996,9 @@ function install_display_output($output, $install_state) {
   $response->headers->add($default_headers);
   $response->setContent($bare_html_page_renderer->renderBarePage($output, $output['#title'], 'install_page', $regions));
 
-  // Prepare attachments, because this does not go the usual way via the
+  // Process attachments, because this does not go the usual way via the
   // Symfony chain, but is sent directly.
-  $bare_html_page_renderer->prepareAttachments($response);
+  $bare_html_page_renderer->processAttachments($response);
 
   $response->send();
   exit;
diff --git a/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php
index 69fc027..b2afa77 100644
--- a/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/HtmlResponseSubscriber.php
@@ -111,7 +111,7 @@ public function onRespond(FilterResponseEvent $event) {
   }
 
   /**
-   * Prorcess attachments contained in a HtmlResponse.
+   * Processes attachments contained in a HtmlResponse.
    *
    * This renders them into HTML markup and replaces the HTML response
    * placeholders in the content of the response.
@@ -131,12 +131,13 @@ public function processAttachments(AttachmentsResponseInterface $response) {
     $variables = [];
     $variables += $this->processAssetLibraries($attached, $placeholders);
 
+    // Handle all non-asset attachments. This populates drupal_get_html_head()
+    // and drupal_get_http_header().
+    $all_attached = ['#attached' => $attached];
+    drupal_process_attached($all_attached);
+
     // Get HTML head elements - if present.
     if (isset($placeholders['head'])) {
-      // Handle all non-asset attachments.
-      $all_attached = ['#attached' => $attached];
-      drupal_process_attached($all_attached);
-
       $variables['head'] = drupal_get_html_head(FALSE);
     }
 
@@ -210,7 +211,9 @@ protected function processAssetLibraries(array $attached, array $placeholders) {
   protected function renderPlaceholders(AttachmentsResponseInterface $response, array $placeholders, array $variables) {
     $content = $response->getContent();
     foreach ($placeholders as $type => $placeholder) {
-      $content = str_replace($placeholder, $this->renderer->renderPlain($variables[$type]), $content);
+      if (isset($variables[$type])) {
+        $content = str_replace($placeholder, $this->renderer->renderPlain($variables[$type]), $content);
+      }
     }
     $response->setContent($content);
   }
diff --git a/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php b/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php
index 98de48f..3ee4d26 100644
--- a/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php
+++ b/core/lib/Drupal/Core/Render/BareHtmlPageRenderer.php
@@ -85,8 +85,8 @@ public function renderBarePage(array $content, $title, $page_theme_property, arr
   /**
    * {@inheritdoc}
    */
-  public function prepareAttachments(AttachmentsResponseInterface $response) {
-    $this->htmlResponseSubscriber->prepareAttachments($response);
+  public function processAttachments(AttachmentsResponseInterface $response) {
+    $this->htmlResponseSubscriber->processAttachments($response);
   }
 
 }