diff --git a/core/lib/Drupal/Core/Routing/RouteBuilder.php b/core/lib/Drupal/Core/Routing/RouteBuilder.php
index 0581ebc..d720f07 100644
--- a/core/lib/Drupal/Core/Routing/RouteBuilder.php
+++ b/core/lib/Drupal/Core/Routing/RouteBuilder.php
@@ -109,6 +109,12 @@ public function rebuild() {
     foreach ($yaml_discovery->findAll() as $provider => $routes) {
       $collection = new RouteCollection();
 
+      // The top-level 'routes_callback' is a list of methods in controller
+      // syntax, see \Drupal\Core\Controller\ControllerResolver. These methods
+      // should return a set of \Symfony\Component\Routing\Route objects, either
+      // in an associative array keyed by the route name, or as a new
+      // \Symfony\Component\Routing\RouteCollection, which will be iterated over
+      // and added to the collection for this provider.
       if (isset($routes['route_callbacks'])) {
         foreach ($routes['route_callbacks'] as $route_callback) {
           $callback = $this->controllerResolver->getControllerFromDefinition($route_callback);
diff --git a/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php b/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
index 9ea2165..98cbfda 100644
--- a/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
+++ b/core/tests/Drupal/Tests/Core/Routing/RouteBuilderTest.php
@@ -8,10 +8,10 @@
 namespace Drupal\Tests\Core\Routing;
 
 use Drupal\Component\Discovery\YamlDiscovery;
+use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Routing\RouteBuilder;
 use Drupal\Core\Routing\RouteBuildEvent;
 use Drupal\Core\Routing\RoutingEvents;
-use Drupal\Tests\Core\Routing\RoutingFixtures;
 use Drupal\Tests\UnitTestCase;
 use Symfony\Component\Routing\Route;
 use Symfony\Component\Routing\RouteCollection;
@@ -203,21 +203,32 @@ public function testRebuildWithProviderBasedRoutes() {
       ->will($this->returnValue(array(
         'test_module' => array(
           'route_callbacks' => array(
-            '\Drupal\Tests\Core\Routing\TestRouteSubscriber::routes',
+            '\Drupal\Tests\Core\Routing\TestRouteSubscriber::routesFromArray',
+            'test_module.route_service:routesFromCollection',
           ),
         ),
       )));
 
+    $container = new ContainerBuilder();
+    $container->set('test_module.route_service', new TestRouteSubscriber());
     $this->controllerResolver->expects($this->any())
       ->method('getControllerFromDefinition')
-      ->will($this->returnCallback(function ($controller) {
-        list($class, $method) = explode('::', $controller, 2);
-        $controller = new $class();
-        return array($controller, $method);
+      ->will($this->returnCallback(function ($controller) use ($container) {
+        $count = substr_count($controller, ':');
+        if ($count == 1) {
+          list($service, $method) = explode(':', $controller, 2);
+          $object = $container->get($service);
+        }
+        else {
+          list($class, $method) = explode('::', $controller, 2);
+          $object = new $class();
+        }
+        return array($object, $method);
       }));
 
     $route_collection_filled = new RouteCollection();
-    $route_collection_filled->add('test_route', new Route('/test-route'));
+    $route_collection_filled->add('test_route.1', new Route('/test-route/1'));
+    $route_collection_filled->add('test_route.2', new Route('/test-route/2'));
 
     // Ensure that the dispatch events for altering are fired.
     $this->dispatcher->expects($this->at(0))
@@ -266,9 +277,14 @@ public function setYamlDiscovery(YamlDiscovery $yaml_discovery) {
  * Provides a callback for route definition.
  */
 class TestRouteSubscriber {
-  public function routes() {
+  public function routesFromArray() {
     return array(
-      'test_route' => new Route('/test-route'),
+      'test_route.1' => new Route('/test-route/1'),
     );
   }
+  public function routesFromCollection() {
+    $collection = new RouteCollection();
+    $collection->add('test_route.2', new Route('/test-route/2'));
+    return $collection;
+  }
 }