diff --git a/core/core.services.yml b/core/core.services.yml
index fc1b515..32bbbd6 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -424,8 +424,7 @@ services:
   theme.negotiator:
     class: Drupal\Core\Theme\ThemeNegotiator
     arguments: ['@access_check.theme']
-    calls:
-      - [setContainer, ['@service_container']]
+    parent: container.trait
     tags:
       - { name: service_id_collector, tag: theme_negotiator }
   theme.negotiator.default:
diff --git a/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php b/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php
index 55a6f7f..ceae0ae 100644
--- a/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php
+++ b/core/tests/Drupal/Tests/Core/Theme/ThemeNegotiatorTest.php
@@ -7,11 +7,10 @@
 
 namespace Drupal\Tests\Core\Theme;
 
+use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\Routing\RouteMatch;
 use Drupal\Core\Theme\ThemeNegotiator;
 use Drupal\Tests\UnitTestCase;
-use Symfony\Component\HttpFoundation\Request;
-use Symfony\Component\HttpFoundation\RequestStack;
 use Symfony\Component\Routing\Route;
 
 /**
@@ -28,6 +27,13 @@ class ThemeNegotiatorTest extends UnitTestCase {
   protected $themeAccessCheck;
 
   /**
+   * The container builder.
+   *
+   * @var \Drupal\Core\DependencyInjection\ContainerBuilder
+   */
+  protected $container;
+
+  /**
    * The request stack.
    *
    * @var \Symfony\Component\HttpFoundation\RequestStack
@@ -41,11 +47,14 @@ class ThemeNegotiatorTest extends UnitTestCase {
    */
   protected $themeNegotiator;
 
+  /**
+   * {@inheritdoc}
+   */
   protected function setUp() {
     $this->themeAccessCheck = $this->getMockBuilder('\Drupal\Core\Theme\ThemeAccessCheck')
       ->disableOriginalConstructor()
       ->getMock();
-    $this->themeNegotiator = new ThemeNegotiator($this->themeAccessCheck);
+    $this->container = new ContainerBuilder();
   }
 
   /**
@@ -62,14 +71,16 @@ public function testDetermineActiveTheme() {
       ->method('applies')
       ->will($this->returnValue(TRUE));
 
-    $this->themeNegotiator->addNegotiator($negotiator, 0);
+    $this->container->set('test_negotiator', $negotiator);
+
+    $negotiators = ['test_negotiator'];
 
     $this->themeAccessCheck->expects($this->any())
       ->method('checkAccess')
       ->will($this->returnValue(TRUE));
 
     $route_match = new RouteMatch('test_route', new Route('/test-route'), array(), array());
-    $theme = $this->themeNegotiator->determineActiveTheme($route_match);
+    $theme = $this->createThemeNegotiator($negotiators)->determineActiveTheme($route_match);
 
     $this->assertEquals('example_test', $theme);
   }
@@ -80,6 +91,8 @@ public function testDetermineActiveTheme() {
    * @see \Drupal\Core\Theme\ThemeNegotiator::determineActiveTheme()
    */
   public function testDetermineActiveThemeWithPriority() {
+    $negotiators = [];
+
     $negotiator = $this->getMock('Drupal\Core\Theme\ThemeNegotiatorInterface');
     $negotiator->expects($this->once())
       ->method('determineActiveTheme')
@@ -88,7 +101,7 @@ public function testDetermineActiveThemeWithPriority() {
       ->method('applies')
       ->will($this->returnValue(TRUE));
 
-    $this->themeNegotiator->addNegotiator($negotiator, 10);
+    $negotiators['test_negotiator_1'] = $negotiator;
 
     $negotiator = $this->getMock('Drupal\Core\Theme\ThemeNegotiatorInterface');
     $negotiator->expects($this->never())
@@ -96,14 +109,18 @@ public function testDetermineActiveThemeWithPriority() {
     $negotiator->expects($this->never())
       ->method('applies');
 
-    $this->themeNegotiator->addNegotiator($negotiator, 0);
+    $negotiators['test_negotiator_2'] = $negotiator;
+
+    foreach ($negotiators as $id => $negotiator) {
+      $this->container->set($id, $negotiator);
+    }
 
     $this->themeAccessCheck->expects($this->any())
       ->method('checkAccess')
       ->will($this->returnValue(TRUE));
 
     $route_match = new RouteMatch('test_route', new Route('/test-route'), array(), array());
-    $theme = $this->themeNegotiator->determineActiveTheme($route_match);
+    $theme = $this->createThemeNegotiator(array_keys($negotiators))->determineActiveTheme($route_match);
 
     $this->assertEquals('example_test', $theme);
   }
@@ -114,6 +131,8 @@ public function testDetermineActiveThemeWithPriority() {
    * @see \Drupal\Core\Theme\ThemeNegotiator::determineActiveTheme()
    */
   public function testDetermineActiveThemeWithAccessCheck() {
+    $negotiators = [];
+
     $negotiator = $this->getMock('Drupal\Core\Theme\ThemeNegotiatorInterface');
     $negotiator->expects($this->once())
       ->method('determineActiveTheme')
@@ -122,7 +141,7 @@ public function testDetermineActiveThemeWithAccessCheck() {
       ->method('applies')
       ->will($this->returnValue(TRUE));
 
-    $this->themeNegotiator->addNegotiator($negotiator, 10);
+    $negotiators['test_negotiator_1'] = $negotiator;
 
     $negotiator = $this->getMock('Drupal\Core\Theme\ThemeNegotiatorInterface');
     $negotiator->expects($this->once())
@@ -132,7 +151,11 @@ public function testDetermineActiveThemeWithAccessCheck() {
       ->method('applies')
       ->will($this->returnValue(TRUE));
 
-    $this->themeNegotiator->addNegotiator($negotiator, 0);
+    $negotiators['test_negotiator_2'] = $negotiator;
+
+    foreach ($negotiators as $id => $negotiator) {
+      $this->container->set($id, $negotiator);
+    }
 
     $this->themeAccessCheck->expects($this->at(0))
       ->method('checkAccess')
@@ -145,7 +168,7 @@ public function testDetermineActiveThemeWithAccessCheck() {
       ->will($this->returnValue(TRUE));
 
     $route_match = new RouteMatch('test_route', new Route('/test-route'), array(), array());
-    $theme = $this->themeNegotiator->determineActiveTheme($route_match);
+    $theme = $this->createThemeNegotiator(array_keys($negotiators))->determineActiveTheme($route_match);
 
     $this->assertEquals('example_test2', $theme);
   }
@@ -156,6 +179,8 @@ public function testDetermineActiveThemeWithAccessCheck() {
    * @see \Drupal\Core\Theme\ThemeNegotiatorInterface
    */
   public function testDetermineActiveThemeWithNotApplyingNegotiator() {
+    $negotiators = [];
+
     $negotiator = $this->getMock('Drupal\Core\Theme\ThemeNegotiatorInterface');
     $negotiator->expects($this->never())
       ->method('determineActiveTheme');
@@ -163,7 +188,7 @@ public function testDetermineActiveThemeWithNotApplyingNegotiator() {
       ->method('applies')
       ->will($this->returnValue(FALSE));
 
-    $this->themeNegotiator->addNegotiator($negotiator, 10);
+    $negotiators['test_negotiator_1'] = $negotiator;
 
     $negotiator = $this->getMock('Drupal\Core\Theme\ThemeNegotiatorInterface');
     $negotiator->expects($this->once())
@@ -173,16 +198,35 @@ public function testDetermineActiveThemeWithNotApplyingNegotiator() {
       ->method('applies')
       ->will($this->returnValue(TRUE));
 
-    $this->themeNegotiator->addNegotiator($negotiator, 0);
+    $negotiators['test_negotiator_2'] = $negotiator;
+
+    foreach ($negotiators as $id => $negotiator) {
+      $this->container->set($id, $negotiator);
+    }
 
     $this->themeAccessCheck->expects($this->any())
       ->method('checkAccess')
       ->will($this->returnValue(TRUE));
 
     $route_match = new RouteMatch('test_route', new Route('/test-route'), array(), array());
-    $theme = $this->themeNegotiator->determineActiveTheme($route_match);
+    $theme = $this->createThemeNegotiator(array_keys($negotiators))->determineActiveTheme($route_match);
 
     $this->assertEquals('example_test2', $theme);
   }
 
+  /**
+   * Creates a new theme negotiator instance.
+   *
+   * @param array $negotiators
+   *   An array of negotiator IDs.
+   *
+   * @return \Drupal\Core\Theme\ThemeNegotiator
+   */
+  protected function createThemeNegotiator(array $negotiators) {
+    $theme_negotiator = new ThemeNegotiator($this->themeAccessCheck, $negotiators);
+    $theme_negotiator->setContainer($this->container);
+
+    return $theme_negotiator;
+  }
+
 }