core/lib/Drupal/Core/Cache/CacheContexts.php                     | 2 +-
 core/lib/Drupal/Core/Cache/ConfigurableCacheContextInterface.php | 6 +++++-
 core/lib/Drupal/Core/Cache/ThemeCacheContext.php                 | 2 +-
 3 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/core/lib/Drupal/Core/Cache/CacheContexts.php b/core/lib/Drupal/Core/Cache/CacheContexts.php
index 3d4a446..19caae0 100644
--- a/core/lib/Drupal/Core/Cache/CacheContexts.php
+++ b/core/lib/Drupal/Core/Cache/CacheContexts.php
@@ -136,7 +136,7 @@ public function getCacheTagsForTokens(array $context_tokens) {
         throw new \InvalidArgumentException(String::format('"@context" is not a valid cache context ID.', ['@context' => $context_id]));
       }
       $service = $this->getService($context_id);
-      if (method_exists($service, 'getCacheTags')) {
+      if ($service instanceof ConfigurableCacheContextInterface) {
         $tags = Cache::mergeTags($service->getCacheTags($parameter));
       }
     }
diff --git a/core/lib/Drupal/Core/Cache/ConfigurableCacheContextInterface.php b/core/lib/Drupal/Core/Cache/ConfigurableCacheContextInterface.php
index 877fe27..d26b65e 100644
--- a/core/lib/Drupal/Core/Cache/ConfigurableCacheContextInterface.php
+++ b/core/lib/Drupal/Core/Cache/ConfigurableCacheContextInterface.php
@@ -15,8 +15,12 @@
   /**
    * The cache tags associated with the cache context.
    *
+   * @param string|null $parameter
+   *   The parameter, in case of a calculated cache context.
+   *
    * @return string[]
+   *   The assocaited cache tags.
    */
-  public function getCacheTags();
+  public function getCacheTags($parameter = NULL);
 
 }
diff --git a/core/lib/Drupal/Core/Cache/ThemeCacheContext.php b/core/lib/Drupal/Core/Cache/ThemeCacheContext.php
index 9620c70..ae3985c 100644
--- a/core/lib/Drupal/Core/Cache/ThemeCacheContext.php
+++ b/core/lib/Drupal/Core/Cache/ThemeCacheContext.php
@@ -13,7 +13,7 @@
 /**
  * Defines the ThemeCacheContext service, for "per theme" caching.
  */
-class ThemeCacheContext implements CacheContextInterface {
+class ThemeCacheContext implements CacheContextInterface, ConfigurableCacheContextInterface {
 
   /**
    * The theme manager.