core/includes/bootstrap.inc                       |    5 ++++-
 core/modules/block/lib/Drupal/block/BlockBase.php |    3 +++
 2 files changed, 7 insertions(+), 1 deletion(-)

diff --git a/core/includes/bootstrap.inc b/core/includes/bootstrap.inc
index eb4b964..7c338d8 100644
--- a/core/includes/bootstrap.inc
+++ b/core/includes/bootstrap.inc
@@ -974,7 +974,10 @@ function drupal_serve_page_from_cache(stdClass $cache, Response $response, Reque
   // max-age > 0, allowing the page to be cached by external proxies, when a
   // session cookie is present unless the Vary header has been replaced.
   $max_age = !$request->cookies->has(session_name()) || isset($boot_headers['vary']) ? $config->get('cache.page.max_age') : 0;
-  // Never set an expiration date further than one year into the future.
+  // RFC 2616, section 14.21 says: 'To mark a response as "never expires," an
+  // origin server sends an Expires date approximately one year from the time
+  // the response is sent. HTTP/1.1 servers SHOULD NOT send Expires dates more
+  // than one year in the future.'
   if ($max_age > 31536000 || $max_age === \Drupal\Core\Cache\Cache::PERMANENT) {
     $max_age = 31536000;
   }
diff --git a/core/modules/block/lib/Drupal/block/BlockBase.php b/core/modules/block/lib/Drupal/block/BlockBase.php
index 768dd70..99150cf 100644
--- a/core/modules/block/lib/Drupal/block/BlockBase.php
+++ b/core/modules/block/lib/Drupal/block/BlockBase.php
@@ -182,6 +182,9 @@ public function blockForm($form, &$form_state) {
    * @see \Drupal\block\BlockBase::blockValidate()
    */
   public function validateConfigurationForm(array &$form, array &$form_state) {
+    // Transform the #type = checkboxes value to a numerically indexed array.
+    $form_state['values']['cache']['contexts'] = array_values(array_filter($form_state['values']['cache']['contexts']));
+
     $this->blockValidate($form, $form_state);
   }