diff -u b/core/modules/node/node.tokens.inc b/core/modules/node/node.tokens.inc
--- b/core/modules/node/node.tokens.inc
+++ b/core/modules/node/node.tokens.inc
@@ -152,7 +152,10 @@
                   $length = $settings['trim_length'];
                 }
 
-                $output = text_summary($output, $item->format, $length);
+                // Cast to string, because "processed" returns a
+                // \Drupal\Component\Render\MarkupInterface via check_markup()
+                // and all unicode utilities expects string input.
+                $output = text_summary((string) $output, $item->format, $length);
               }
             }
             // "processed" returns a \Drupal\Component\Render\MarkupInterface
diff -u b/core/modules/node/tests/src/Kernel/NodeTokenReplaceTest.php b/core/modules/node/tests/src/Kernel/NodeTokenReplaceTest.php
--- b/core/modules/node/tests/src/Kernel/NodeTokenReplaceTest.php
+++ b/core/modules/node/tests/src/Kernel/NodeTokenReplaceTest.php
@@ -142,8 +142,8 @@
 
     // Get teaser node view display.
     $view_display = \Drupal::entityTypeManager()
-        ->getStorage('entity_view_display')
-        ->load('node.article.teaser');
+      ->getStorage('entity_view_display')
+      ->load('node.article.teaser');
     if (!$view_display) {
       $values = [
         'targetEntityType' => 'node',
@@ -152,8 +152,8 @@
         'status' => TRUE,
       ];
       $view_display = \Drupal::entityTypeManager()
-          ->getStorage('entity_view_display')
-          ->create($values);
+        ->getStorage('entity_view_display')
+        ->create($values);
     }
 
     // Token [node:summary] should use trim settings of "Summary or trimmed"