diff --git a/core/lib/Drupal/Core/Config/ConfigBase.php b/core/lib/Drupal/Core/Config/ConfigBase.php
index 556926d..e88560e 100644
--- a/core/lib/Drupal/Core/Config/ConfigBase.php
+++ b/core/lib/Drupal/Core/Config/ConfigBase.php
@@ -65,7 +65,7 @@
    *
    * @var int
    */
-  protected $cacheMaxAge;
+  protected $cacheMaxAge = Cache::PERMANENT;
 
   /**
    * The maximum length of a configuration object name.
@@ -298,14 +298,14 @@ public function getCacheContexts() {
    * {@inheritdoc}
    */
   public function getCacheTags() {
-    return ['config:' . $this->name];
+    return Cache::mergeTags(['config:' . $this->name], $this->cacheTags);
   }
 
   /**
    * {@inheritdoc}
    */
   public function getCacheMaxAge() {
-    return Cache::PERMANENT;
+    return $this->cacheMaxAge;
   }
 
   /**
diff --git a/core/modules/config/src/Tests/CacheContextConfigOverrideTest.php b/core/modules/config/src/Tests/CacheContextConfigOverrideTest.php
index 00ce58b..38cbb42 100644
--- a/core/modules/config/src/Tests/CacheContextConfigOverrideTest.php
+++ b/core/modules/config/src/Tests/CacheContextConfigOverrideTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\config\Tests;
 
+use Drupal\Core\Cache\Cache;
 use Drupal\simpletest\KernelTestBase;
 
 /**
@@ -23,15 +24,19 @@ class CacheContextConfigOverrideTest extends KernelTestBase {
 
   public function testConfigOverride() {
     // It's pirate day today!
-    $GLOBALS['arr_me_mateys'] = TRUE;
+    $GLOBALS['it_is_pirate_day'] = TRUE;
 
     $config_factory = $this->container->get('config.factory');
     $config = $config_factory->get('system.theme');
-    $theme = $config->get('default');
 
+    // Check that we are using the Pirate theme.
+    $theme = $config->get('default');
     $this->assertEqual('pirate', $theme);
 
-    $this->assertEquals(['pirate_day'], $config->getCacheContexts);
+    // Check that the cacheable properties are correct.
+    $this->assertEqual(['pirate_day'], $config->getCacheContexts());
+    $this->assertEqual(['config:system.theme'], $config->getCacheTags());
+    $this->assertEqual(Cache::PERMANENT, $config->getCacheMaxAge());
   }
 
 }
diff --git a/core/modules/config/tests/config_override_test/config_override_test.services.yml b/core/modules/config/tests/config_override_test/config_override_test.services.yml
index 88f3550..886b7fd 100644
--- a/core/modules/config/tests/config_override_test/config_override_test.services.yml
+++ b/core/modules/config/tests/config_override_test/config_override_test.services.yml
@@ -1,4 +1,8 @@
 services:
+  cache_context.pirate_day:
+    class: Drupal\config_override_test\Cache\PirateDayCacheContext
+    tags:
+      - { name: cache.context }
   config_override_test.overrider:
     class: Drupal\config_override_test\ConfigOverrider
     tags:
diff --git a/core/modules/config/tests/config_override_test/src/Cache/PirateDayCacheContext.php b/core/modules/config/tests/config_override_test/src/Cache/PirateDayCacheContext.php
new file mode 100644
index 0000000..44c344f
--- /dev/null
+++ b/core/modules/config/tests/config_override_test/src/Cache/PirateDayCacheContext.php
@@ -0,0 +1,47 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\config_override_test\Cache\PirateDayCacheContext.
+ */
+
+namespace Drupal\config_override_test\Cache;
+
+use Drupal\Core\Cache\Context\CacheContextInterface;
+
+/**
+ * Defines the PirateDayCacheContext service that allows to cache the booty.
+ *
+ * Cache context ID: 'pirate_day'.
+ */
+class PirateDayCacheContext implements CacheContextInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function getLabel() {
+    return t('Pirate day');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getContext() {
+    $is_pirate_day = static::isPirateDay() ? 'yarr' : 'nay';
+    return "pirate_day." . $is_pirate_day;
+  }
+
+  /**
+   * Returns whether or not it is Pirate Day.
+   *
+   * To ease testing this is determined with a global variable rather than using
+   * the traditional compass and sextant.
+   *
+   * @return bool
+   *   Returns TRUE if it is Pirate Day today.
+   */
+  public static function isPirateDay() {
+    return !empty($GLOBALS['it_is_pirate_day']);
+  }
+
+}
diff --git a/core/modules/config/tests/config_override_test/src/PirateDayCacheContextConfigOverride.php b/core/modules/config/tests/config_override_test/src/PirateDayCacheContextConfigOverride.php
index 47f7581..20f8303 100644
--- a/core/modules/config/tests/config_override_test/src/PirateDayCacheContextConfigOverride.php
+++ b/core/modules/config/tests/config_override_test/src/PirateDayCacheContextConfigOverride.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\config_override_test;
 
+use Drupal\config_override_test\Cache\PirateDayCacheContext;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Config\ConfigFactoryOverrideInterface;
 use Drupal\Core\Config\StorageInterface;
@@ -22,7 +23,7 @@ class PirateDayCacheContextConfigOverride implements ConfigFactoryOverrideInterf
   public function loadOverrides($names) {
     $overrides = array();
 
-    $it_is_pirate_day = $GLOBALS['arr_me_mateys'];
+    $it_is_pirate_day = PirateDayCacheContext::isPirateDay();
     if (in_array('system.theme', $names) && $it_is_pirate_day) {
       $overrides = $overrides + ['system.theme' => ['default' => 'pirate']];
     }
@@ -55,8 +56,6 @@ public function getCacheContexts() {
    * {@inheritdoc}
    */
   public function getCacheTags() {
-    // @todo This is here because we now implement CacheableDependencyInterface,
-    //   but this is not used.
     return [];
   }
 
@@ -64,8 +63,6 @@ public function getCacheTags() {
    * {@inheritdoc}
    */
   public function getCacheMaxAge() {
-    // @todo This is here because we now implement CacheableDependencyInterface,
-    //   but this is not used.
     return Cache::PERMANENT;
   }