core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php |  6 ++----
 .../block/src/Plugin/DisplayVariant/FullPageVariant.php    | 14 +++++++++++++-
 2 files changed, 15 insertions(+), 5 deletions(-)

diff --git a/core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php b/core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php
index df1b52a..3c05cf3 100644
--- a/core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php
+++ b/core/lib/Drupal/Core/Display/Annotation/DisplayVariant.php
@@ -25,10 +25,8 @@
  *
  * Plugin namespace: Plugin\DisplayVariant
  *
- * For working examples, see
- * - \Drupal\system\Plugin\DisplayVariant\SimplePageVariant
- * - \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
- * - \Drupal\block\Plugin\DisplayVariant\DemoBlockPageVariant
+ * For a working example, see
+ * \Drupal\block\Plugin\DisplayVariant\FullPageVariant
  *
  * @see \Drupal\Core\Display\VariantInterface
  * @see \Drupal\Core\Display\VariantBase
diff --git a/core/modules/block/src/Plugin/DisplayVariant/FullPageVariant.php b/core/modules/block/src/Plugin/DisplayVariant/FullPageVariant.php
index dc91b8b..a927dd4 100644
--- a/core/modules/block/src/Plugin/DisplayVariant/FullPageVariant.php
+++ b/core/modules/block/src/Plugin/DisplayVariant/FullPageVariant.php
@@ -20,7 +20,7 @@
 /**
  * Provides a display variant that represents the full page.
  *
- * @DisplayVariant(
+ * @PageDisplayVariant(
  *   id = "full_page",
  *   admin_label = @Translation("Full page")
  * )
@@ -132,6 +132,9 @@ protected function getTheme() {
    * {@inheritdoc}
    */
   public function build() {
+    // Track whether a block that shows the main content is displayed or not.
+    $main_content_block_displayed = FALSE;
+
     $build = array();
     // Load all region content assigned via blocks.
     foreach ($this->getRegionAssignments() as $region => $blocks) {
@@ -140,6 +143,7 @@ public function build() {
         if ($block->access('view')) {
           if ($block->getPlugin() instanceof MainContentBlockPluginInterface) {
             $block->getPlugin()->setMainContent($this->mainContent);
+            $main_content_block_displayed = TRUE;
           }
           $build[$region][$key] = $this->blockViewBuilder->view($block);
         }
@@ -149,6 +153,14 @@ public function build() {
         $build[$region]['#sorted'] = TRUE;
       }
     }
+
+    // If no block that shows the main content is displayed, still show the main
+    // content. Otherwise the end user will see all displayed blocks, but not
+    // the main content they came for.
+    if (!$main_content_block_displayed) {
+      $build['content']['system_main'] = $this->mainContent;
+    }
+
     return $build;
   }