diff --git a/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php b/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
index 6829939..ac5e151 100644
--- a/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
+++ b/core/modules/system/lib/Drupal/system/Tests/Menu/MenuRouterTest.php
@@ -614,4 +614,18 @@ function testMenuLoadArgumentsInheritance() {
       $this->assertIdentical(unserialize($router_item['load_functions']), $load_functions, format_string('Expected load functions for router %router_path' , array('%router_path' => $router_path)));
     }
   }
+
+  /**
+   * Test menu links that have optional placeholders.
+   */
+  public function testMenuOptionalPlaceholders() {
+    $this->drupalGet('menu-test/optional');
+    $this->assertResponse(200);
+    $this->assertText('Sometimes there is no placeholder.');
+
+    $this->drupalGet('menu-test/optional/foobar');
+    $this->assertResponse(200);
+    $this->assertText("Sometimes there is a placeholder: 'foobar'.");
+  }
+
 }
diff --git a/core/modules/system/tests/modules/menu_test/lib/Drupal/menu_test/TestControllers.php b/core/modules/system/tests/modules/menu_test/lib/Drupal/menu_test/TestControllers.php
index 48c2da3..c36a0ae 100644
--- a/core/modules/system/tests/modules/menu_test/lib/Drupal/menu_test/TestControllers.php
+++ b/core/modules/system/tests/modules/menu_test/lib/Drupal/menu_test/TestControllers.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\menu_test;
 
+use Drupal\Component\Utility\String;
 use Drupal\Core\Entity\EntityInterface;
 
 /**
@@ -35,4 +36,22 @@ public function test2() {
     return 'test2';
   }
 
+  /**
+   * Prints out test data.
+   *
+   * @param string|null $placeholder
+   *   A placeholder for the return string.
+   *
+   * @return string
+   *   The string for this route.
+   */
+  public function testDefaults($placeholder = NULL) {
+    if ($placeholder) {
+      return String::format("Sometimes there is a placeholder: '@placeholder'.", array('@placeholder' => $placeholder));
+    }
+    else {
+      return String::format('Sometimes there is no placeholder.');
+    }
+  }
+
 }
diff --git a/core/modules/system/tests/modules/menu_test/menu_test.module b/core/modules/system/tests/modules/menu_test/menu_test.module
index eb43fdf..8f71bd3 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.module
+++ b/core/modules/system/tests/modules/menu_test/menu_test.module
@@ -438,6 +438,11 @@ function menu_test_menu() {
     'title' => 'Local tasks',
     'route_name' => 'menu_local_task_test_tasks',
   );
+  $items['menu-test/optional'] = array(
+    'title' => 'Test optional placeholder',
+    'route_name' => 'menu_test_optional_placeholder',
+    'type' => MENU_LOCAL_TASK,
+  );
 
   return $items;
 }
diff --git a/core/modules/system/tests/modules/menu_test/menu_test.routing.yml b/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
index 4eee7ed..9cf8f11 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
+++ b/core/modules/system/tests/modules/menu_test/menu_test.routing.yml
@@ -99,3 +99,11 @@ menu_local_task_test_tasks_settings_sub2:
     _content: '\Drupal\menu_test\TestControllers::test1'
   requirements:
     _access: 'TRUE'
+
+menu_test_optional_placeholder:
+  pattern: '/menu-test/optional/{placeholder}'
+  defaults:
+    _content: '\Drupal\menu_test\TestControllers::testDefaults'
+    placeholder: ~
+  requirements:
+    _access: 'TRUE'