diff --git a/core/modules/comment/src/Plugin/Field/FieldFormatter/CommentDefaultFormatter.php b/core/modules/comment/src/Plugin/Field/FieldFormatter/CommentDefaultFormatter.php
index ad5149f..cdd68f6 100644
--- a/core/modules/comment/src/Plugin/Field/FieldFormatter/CommentDefaultFormatter.php
+++ b/core/modules/comment/src/Plugin/Field/FieldFormatter/CommentDefaultFormatter.php
@@ -239,7 +239,10 @@ public function settingsForm(array $form, FormStateInterface $form_state) {
    * {@inheritdoc}
    */
   public function settingsSummary() {
-    $summary = [$this->t('Comment view mode: @mode', ['@mode' => $this->getViewModes()[$this->getSetting('view_mode')]])];
+    $view_mode = $this->getSetting('view_mode');
+    $view_modes = $this->getViewModes();
+    $view_mode_label = isset($view_modes[$view_mode]) ? $view_modes[$view_mode] : 'default';
+    $summary = [$this->t('Comment view mode: @mode', ['@mode' => $view_mode_label])];
     if ($pager_id = $this->getSetting('pager_id')) {
       $summary[] = $this->t('Pager ID: @id', ['@id' => $pager_id]);
     }
diff --git a/core/modules/comment/src/Tests/CommentPagerTest.php b/core/modules/comment/src/Tests/CommentPagerTest.php
index 9061f64..14cd3b5 100644
--- a/core/modules/comment/src/Tests/CommentPagerTest.php
+++ b/core/modules/comment/src/Tests/CommentPagerTest.php
@@ -288,6 +288,7 @@ function testTwoPagers() {
         'weight' => 30,
         'settings' => array(
           'pager_id' => 1,
+          'view_mode' => 'default',
         )
       ))
       ->save();