diff --git a/core/modules/block/src/BlockAccessControlHandler.php b/core/modules/block/src/BlockAccessControlHandler.php
index dbe866f..4529647 100644
--- a/core/modules/block/src/BlockAccessControlHandler.php
+++ b/core/modules/block/src/BlockAccessControlHandler.php
@@ -138,7 +138,10 @@ protected function checkAccess(EntityInterface $entity, $operation, AccountInter
         catch (ContextException $e) {
           // Setting access to forbidden if any context is missing for the same
           // reasons as with conditions (described in the comment above).
-          $access = AccessResult::forbidden();
+          // @todo Avoid setting max-age 0 for some or all cases, for example by
+          //   treating available contexts without value differently in
+          //   https://www.drupal.org/node/2521956.
+          $access = AccessResult::forbidden()->setCacheMaxAge(0);
         }
       }
       else {