diff --git a/core/modules/user/src/ToolbarLinkBuilder.php b/core/modules/user/src/ToolbarLinkBuilder.php
index b278db6dba4c253220e58b28194d921436cf96e3..8d989b339e5232f7c8fc2bd3975509671f19191c 100644
--- a/core/modules/user/src/ToolbarLinkBuilder.php
+++ b/core/modules/user/src/ToolbarLinkBuilder.php
@@ -80,7 +80,7 @@ public function renderToolbarLinks() {
    */
   public function renderDisplayName() {
     return [
-      '#markup' => $this->account->getDisplayName(),
+      '#plain_text' => $this->account->getDisplayName(),
     ];
   }
 
diff --git a/core/modules/user/tests/src/Unit/ToolbarLinkBuilderTest.php b/core/modules/user/tests/src/Unit/ToolbarLinkBuilderTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..40be72a666452f733e36613c7b9c60e06fde3e62
--- /dev/null
+++ b/core/modules/user/tests/src/Unit/ToolbarLinkBuilderTest.php
@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\Tests\user\Unit;
+
+use Drupal\Core\Session\AccountProxyInterface;
+use Drupal\Tests\UnitTestCase;
+use Drupal\user\ToolbarLinkBuilder;
+
+/**
+ * Tests user's ToolbarLinkBuilder.
+ *
+ * @coversDefaultClass \Drupal\user\ToolbarLinkBuilder
+ * @group user
+ */
+class ToolbarLinkBuilderTest extends UnitTestCase {
+
+  /**
+   * Tests structure of display name render array.
+   *
+   * @covers ::renderDisplayName
+   */
+  public function testRenderDisplayName() {
+    $account = $this->prophesize(AccountProxyInterface::class);
+    $display_name = 'Something suspicious that should be #plain_text, not #markup';
+    $account->getDisplayName()->willReturn($display_name);
+    $toolbar_link_builder = new ToolbarLinkBuilder($account->reveal());
+    $expected = ['#plain_text' => $display_name];
+    $this->assertSame($expected, $toolbar_link_builder->renderDisplayName());
+  }
+
+}