core/lib/Drupal/Core/Cache/CacheBackendInterface.php             |    2 +-
 core/modules/block/lib/Drupal/block/BlockBase.php                |    2 +-
 core/modules/block/lib/Drupal/block/BlockViewBuilder.php         |    3 ++-
 core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php |    2 +-
 4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/core/lib/Drupal/Core/Cache/CacheBackendInterface.php b/core/lib/Drupal/Core/Cache/CacheBackendInterface.php
index 3bdbc64..36fd5a3 100644
--- a/core/lib/Drupal/Core/Cache/CacheBackendInterface.php
+++ b/core/lib/Drupal/Core/Cache/CacheBackendInterface.php
@@ -74,7 +74,7 @@
   /**
    * Indicates that the item should never be removed unless explicitly deleted.
    */
-  const CACHE_PERMANENT = 0;
+  const CACHE_PERMANENT = -1;
 
   /**
    * Returns data from the persistent cache.
diff --git a/core/modules/block/lib/Drupal/block/BlockBase.php b/core/modules/block/lib/Drupal/block/BlockBase.php
index 5b7986c..8185a18 100644
--- a/core/modules/block/lib/Drupal/block/BlockBase.php
+++ b/core/modules/block/lib/Drupal/block/BlockBase.php
@@ -115,7 +115,7 @@ public function buildConfigurationForm(array $form, array &$form_state) {
     );
     $ages = array(0, 60, 300, 1800, 3600, 21600, 86400, 604800, 2592000, 31536000);
     $options = array_map(array(\Drupal::service('date'), 'formatInterval'), array_combine($ages, $ages));
-    $options[-1] = t('Forever');
+    $options[\Drupal\Core\Cache\Cache::PERMANENT] = t('Forever');
     $form['cache']['max_age'] = array(
       '#type' => 'select',
       '#title' => t('Cache: Max age'),
diff --git a/core/modules/block/lib/Drupal/block/BlockViewBuilder.php b/core/modules/block/lib/Drupal/block/BlockViewBuilder.php
index d6e5056..6fe8abc 100644
--- a/core/modules/block/lib/Drupal/block/BlockViewBuilder.php
+++ b/core/modules/block/lib/Drupal/block/BlockViewBuilder.php
@@ -83,10 +83,11 @@ public function viewMultiple(array $entities = array(), $view_mode = 'full', $la
         // Generic cache keys, with the block plugin's custom keys appended
         // (usually cache context keys like DRUPAL_CACHE_PER_ROLE).
         $default_cache_keys = array('entity_view', 'block', $entity->id(), $entity->langcode);
+        $max_age = $plugin->getCacheMaxAge();
         $build[$entity_id]['#cache'] += array(
           'keys' => array_merge($default_cache_keys, $plugin->getCacheKeys()),
           'bin' => $plugin->getCacheBin(),
-          'expire' => REQUEST_TIME + $plugin->getCacheMaxAge(),
+          'expire' => ($max_age === Cache::PERMANENT) ? Cache::PERMANENT : REQUEST_TIME + $max_age,
         );
       }
       else {
diff --git a/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php b/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php
index 628a7bf..f9c0921 100644
--- a/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php
+++ b/core/modules/block/lib/Drupal/block/Tests/BlockInterfaceTest.php
@@ -64,7 +64,7 @@ public function testBlockInterface() {
 
     $ages = array(0, 60, 300, 1800, 3600, 21600, 86400, 604800, 2592000, 31536000);
     $options = array_map(array(\Drupal::service('date'), 'formatInterval'), array_combine($ages, $ages));
-    $options[-1] = t('Forever');
+    $options[\Drupal\Core\Cache\Cache::PERMANENT] = t('Forever');
     $expected_form = array(
       'module' => array(
         '#type' => 'value',