diff -u b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbBuilderInterface.php b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbBuilderInterface.php
--- b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbBuilderInterface.php
+++ b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbBuilderInterface.php
@@ -32,7 +32,7 @@
    * @param \Drupal\Core\Routing\RouteMatchInterface $route_match
    *   The current route match.
    *
-   * @return \Drupal\Core\Breadcrumb\Breadcrumb
+   * @return mixed[]
    *   A breadcrumb.
    */
   public function build(RouteMatchInterface $route_match);
diff -u b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbManager.php b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbManager.php
--- b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbManager.php
+++ b/core/lib/Drupal/Core/Breadcrumb/BreadcrumbManager.php
@@ -7,7 +7,6 @@
 
 namespace Drupal\Core\Breadcrumb;
 
-use \Drupal\Core\Breadcrumb\Breadcrumb;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Drupal\Core\Routing\RouteMatchInterface;
@@ -77,7 +76,9 @@
    * {@inheritdoc}
    */
   public function build(RouteMatchInterface $route_match) {
-    $breadcrumb = array();
+    $build = [
+      'links' => [],
+    ];
     $context = array('builder' => NULL);
     // Call the build method of registered breadcrumb builders,
     // until one of them returns an array.
@@ -87,12 +88,12 @@
         continue;
       }
 
-      $build = $builder->build($route_match);
+      $breadcrumb = $builder->build($route_match);
 
-      if ($build instanceof Breadcrumb) {
+      if ($breadcrumb instanceof Breadcrumb) {
         // The builder returned an array of breadcrumb links.
-        $breadcrumb['contexts'] = $build->getCacheContexts();
-        $breadcrumb['links'] = $build->getLinks();
+        $build['contexts'] = $breadcrumb->getCacheContexts();
+        $build['links'] = $breadcrumb->getLinks();
         $context['builder'] = $builder;
         break;
       }
@@ -101,9 +102,9 @@
       }
     }
     // Allow modules to alter the breadcrumb.
-    $this->moduleHandler->alter('system_breadcrumb', $breadcrumb['links'], $route_match, $context);
+    $this->moduleHandler->alter('system_breadcrumb', $build['links'], $route_match, $context);
     // Fall back to an empty breadcrumb.
-    return $breadcrumb;
+    return $build;
   }
 
   /**
only in patch2:
unchanged:
--- a/core/modules/forum/tests/src/Unit/Breadcrumb/ForumBreadcrumbBuilderBaseTest.php
+++ b/core/modules/forum/tests/src/Unit/Breadcrumb/ForumBreadcrumbBuilderBaseTest.php
@@ -128,7 +128,7 @@ public function testBuild() {
     );
 
     // And finally, the test.
-    $this->assertEquals($expected, $breadcrumb_builder->build($route_match));
+    $this->assertEquals($expected, $breadcrumb_builder->build($route_match)->getLinks());
   }
 
 }
only in patch2:
unchanged:
--- a/core/tests/Drupal/Tests/Core/Breadcrumb/BreadcrumbManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Breadcrumb/BreadcrumbManagerTest.php
@@ -7,6 +7,7 @@
 
 namespace Drupal\Tests\Core\Breadcrumb;
 
+use Drupal\Core\Breadcrumb\Breadcrumb;
 use Drupal\Core\Breadcrumb\BreadcrumbManager;
 use Drupal\Tests\UnitTestCase;
 
@@ -17,6 +18,13 @@
 class BreadcrumbManagerTest extends UnitTestCase {
 
   /**
+   * The breadcrumb object.
+   *
+   * @var \Drupal\Core\Breadcrumb\Breadcrumb
+   */
+  protected $breadcrumb;
+
+  /**
    * The tested breadcrumb manager.
    *
    * @var \Drupal\Core\Breadcrumb\BreadcrumbManager
@@ -36,6 +44,7 @@ class BreadcrumbManagerTest extends UnitTestCase {
   protected function setUp() {
     $this->moduleHandler = $this->getMock('Drupal\Core\Extension\ModuleHandlerInterface');
     $this->breadcrumbManager = new BreadcrumbManager($this->moduleHandler);
+    $this->breadcrumb = new Breadcrumb();
   }
 
   /**
@@ -43,7 +52,7 @@ protected function setUp() {
    */
   public function testBuildWithoutBuilder() {
     $result = $this->breadcrumbManager->build($this->getMock('Drupal\Core\Routing\RouteMatchInterface'));
-    $this->assertEquals(array(), $result);
+    $this->assertEquals(array(), $result['links']);
   }
 
   /**
@@ -51,7 +60,8 @@ public function testBuildWithoutBuilder() {
    */
   public function testBuildWithSingleBuilder() {
     $builder = $this->getMock('Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface');
-    $breadcrumb = array('<a href="/example">Test</a>');
+    $links = array('<a href="/example">Test</a>');
+    $this->breadcrumb->setLinks($links);
 
     $builder->expects($this->once())
       ->method('applies')
@@ -59,17 +69,17 @@ public function testBuildWithSingleBuilder() {
 
     $builder->expects($this->once())
       ->method('build')
-      ->will($this->returnValue($breadcrumb));
+      ->willReturn($this->breadcrumb);
 
     $route_match = $this->getMock('Drupal\Core\Routing\RouteMatchInterface');
     $this->moduleHandler->expects($this->once())
       ->method('alter')
-      ->with('system_breadcrumb', $breadcrumb, $route_match, array('builder' => $builder));
+      ->with('system_breadcrumb', $links, $route_match, array('builder' => $builder));
 
     $this->breadcrumbManager->addBuilder($builder, 0);
 
     $result = $this->breadcrumbManager->build($route_match);
-    $this->assertEquals($breadcrumb, $result);
+    $this->assertEquals($links, $result['links']);
   }
 
   /**
@@ -83,25 +93,26 @@ public function testBuildWithMultipleApplyingBuilders() {
       ->method('build');
 
     $builder2 = $this->getMock('Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface');
-    $breadcrumb2 = array('<a href="/example2">Test2</a>');
+    $links2 = array('<a href="/example2">Test2</a>');
+    $this->breadcrumb->setLinks($links2);
     $builder2->expects($this->once())
       ->method('applies')
       ->will($this->returnValue(TRUE));
     $builder2->expects($this->once())
       ->method('build')
-      ->will($this->returnValue($breadcrumb2));
+      ->willReturn($this->breadcrumb);
 
     $route_match = $this->getMock('Drupal\Core\Routing\RouteMatchInterface');
 
     $this->moduleHandler->expects($this->once())
       ->method('alter')
-      ->with('system_breadcrumb', $breadcrumb2, $route_match, array('builder' => $builder2));
+      ->with('system_breadcrumb', $links2, $route_match, array('builder' => $builder2));
 
     $this->breadcrumbManager->addBuilder($builder1, 0);
     $this->breadcrumbManager->addBuilder($builder2, 10);
 
     $result = $this->breadcrumbManager->build($route_match);
-    $this->assertEquals($breadcrumb2, $result);
+    $this->assertEquals($links2, $result['links']);
   }
 
   /**
@@ -116,25 +127,26 @@ public function testBuildWithOneNotApplyingBuilders() {
       ->method('build');
 
     $builder2 = $this->getMock('Drupal\Core\Breadcrumb\BreadcrumbBuilderInterface');
-    $breadcrumb2 = array('<a href="/example2">Test2</a>');
+    $links2 = array('<a href="/example2">Test2</a>');
+    $this->breadcrumb->setLinks($links2);
     $builder2->expects($this->once())
       ->method('applies')
       ->will($this->returnValue(TRUE));
     $builder2->expects($this->once())
       ->method('build')
-      ->will($this->returnValue($breadcrumb2));
+      ->willReturn($this->breadcrumb);
 
     $route_match = $this->getMock('Drupal\Core\Routing\RouteMatchInterface');
 
     $this->moduleHandler->expects($this->once())
       ->method('alter')
-      ->with('system_breadcrumb', $breadcrumb2, $route_match, array('builder' => $builder2));
+      ->with('system_breadcrumb', $links2, $route_match, array('builder' => $builder2));
 
     $this->breadcrumbManager->addBuilder($builder1, 10);
     $this->breadcrumbManager->addBuilder($builder2, 0);
 
     $result = $this->breadcrumbManager->build($route_match);
-    $this->assertEquals($breadcrumb2, $result);
+    $this->assertEquals($links2, $result['links']);
   }
 
   /**