.../modules/system/src/Plugin/Block/SystemMainBlock.php | 17 +++++------------
 1 file changed, 5 insertions(+), 12 deletions(-)

diff --git a/core/modules/system/src/Plugin/Block/SystemMainBlock.php b/core/modules/system/src/Plugin/Block/SystemMainBlock.php
index 3d2d45e..aa63110 100644
--- a/core/modules/system/src/Plugin/Block/SystemMainBlock.php
+++ b/core/modules/system/src/Plugin/Block/SystemMainBlock.php
@@ -9,6 +9,7 @@
 
 use Drupal\Core\Block\BlockBase;
 use Drupal\Core\Block\MainContentBlockPluginInterface;
+use Drupal\Core\Cache\Cache;
 use Drupal\Core\Form\FormStateInterface;
 
 /**
@@ -45,23 +46,15 @@ public function build() {
   /**
    * {@inheritdoc}
    */
-  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
-    $form = parent::buildConfigurationForm($form, $form_state);
-
-    // The main content block is never cacheable, because it may be dynamic.
-    $form['cache']['#disabled'] = TRUE;
-    $form['cache']['#description'] = $this->t('This block is never cacheable, it is not configurable.');
-    $form['cache']['max_age']['#value'] = 0;
-
-    return $form;
+  public function getCacheMaxAge() {
+    return Cache::PERMANENT;
   }
 
   /**
    * {@inheritdoc}
    */
-  public function getCacheMaxAge() {
-    // The main content block is never cacheable, because it may be dynamic.
-    return 0;
+  public function getCacheContexts() {
+    return ['route'];
   }
 
 }