core/includes/common.inc                           |    2 +-
 .../Core/EventSubscriber/HtmlViewSubscriber.php    |   40 ++++++++++++++++++--
 2 files changed, 37 insertions(+), 5 deletions(-)

diff --git a/core/includes/common.inc b/core/includes/common.inc
index 12830e5..2d6753c 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -3241,7 +3241,7 @@ function drupal_page_set_cache(Response $response, Request $request) {
         // because by the time it is read, the configuration might change.
         'page_compressed' => $page_compressed,
       ),
-      'tags' => explode(' ', $response->headers->get('X-Drupal-Cache-Tags')),
+      'tags' => Drupal\Core\EventSubscriber\HtmlViewSubscriber::convertHeaderToCacheTags($response->headers->get('X-Drupal-Cache-Tags')),
       'expire' => Cache::PERMANENT,
       'created' => REQUEST_TIME,
     );
diff --git a/core/lib/Drupal/Core/EventSubscriber/HtmlViewSubscriber.php b/core/lib/Drupal/Core/EventSubscriber/HtmlViewSubscriber.php
index c71d86a..4da4d43 100644
--- a/core/lib/Drupal/Core/EventSubscriber/HtmlViewSubscriber.php
+++ b/core/lib/Drupal/Core/EventSubscriber/HtmlViewSubscriber.php
@@ -77,7 +77,7 @@ public function onHtmlPage(GetResponseForControllerResultEvent $event) {
       // recommended.
       $response = new Response((string) $this->pageRenderer->render($page), $page->getStatusCode());
       if ($tags = $page->getCacheTags()) {
-        $response->headers->set('X-Drupal-Cache-Tags', $this->flattenCacheTags($tags));
+        $response->headers->set('X-Drupal-Cache-Tags', $this->convertCacheTagsToHeader($tags));
       }
       if ($keys = $page->getCacheKeys()) {
         $response->headers->set('cache_keys', serialize($keys));
@@ -106,15 +106,15 @@ static function getSubscribedEvents() {
   }
 
   /**
-   * 'Flattens' a tags array into an array of strings.
+   * Converts a cache tags array into a X-Drupal-Cache-Tags header value.
    *
    * @param array $tags
    *   Associative array of cache tags to flatten.
    *
    * @return string
-   *   A space-separated liste of flattened cache tag identifiers.
+   *   A space-separated list of flattened cache tag identifiers.
    */
-  protected function flattenCacheTags(array $tags) {
+  public static function convertCacheTagsToHeader(array $tags) {
     $flat_tags = array();
     foreach ($tags as $namespace => $values) {
       if (is_array($values)) {
@@ -129,4 +129,36 @@ protected function flattenCacheTags(array $tags) {
     return implode(' ', $flat_tags);
   }
 
+  /**
+   * 'Flattens' a tags array into an array of strings.
+   *
+   * @param string $tags
+   *   A space-separated list of flattened cache tag identifiers.
+   *
+   * @return array
+   *   Associative array of cache tags to flatten.
+   */
+  public static function convertHeaderToCacheTags($tags_header) {
+    if (!is_string($tags_header) || strlen(trim($tags_header)) == 0) {
+      return array();
+    }
+
+    $flat_tags = explode(' ', trim($tags_header));
+    $tags = array();
+    foreach ($flat_tags as $flat_tag) {
+      list($namespace, $value) = explode(':', $flat_tag);
+      if (!isset($tags[$namespace])) {
+        $tags[$namespace] = $value;
+      }
+      // Multiple values in this namespace.
+      else {
+        if (!is_array($tags[$namespace])) {
+          $tags[$namespace] = array($tags[$namespace]);
+        }
+        $tags[$namespace][] = $value;
+      }
+    }
+    return $tags;
+  }
+
 }