diff -u b/core/core.services.yml b/core/core.services.yml
--- b/core/core.services.yml
+++ b/core/core.services.yml
@@ -1322,7 +1322,8 @@
     tags:
       - { name: twig.extension, priority: 100 }
     calls:
-      - [setGenerators, ['@url_generator', '@theme.manager']]
+      - [setGenerators, ['@url_generator']]
+      - [setThemeManager, ['@theme.manager']]
   # @todo Figure out what to do about debugging functions.
   # @see https://www.drupal.org/node/1804998
   twig.extension.debug:
diff -u b/core/lib/Drupal/Core/Template/TwigExtension.php b/core/lib/Drupal/Core/Template/TwigExtension.php
--- b/core/lib/Drupal/Core/Template/TwigExtension.php
+++ b/core/lib/Drupal/Core/Template/TwigExtension.php
@@ -66,8 +66,20 @@
    *
    * @return $this
    */
-  public function setGenerators(UrlGeneratorInterface $url_generator, ThemeManagerInterface $theme_manager) {
+  public function setGenerators(UrlGeneratorInterface $url_generator) {
     $this->urlGenerator = $url_generator;
+    return $this;
+  }
+
+  /**
+   * Sets the theme manager.
+   *
+   * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
+   *   The theme manager.
+   *
+   * @return $this
+   */
+  public function setThemeManager(ThemeManagerInterface $theme_manager) {
     $this->themeManager = $theme_manager;
     return $this;
   }
diff -u b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
--- b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
+++ b/core/tests/Drupal/Tests/Core/Template/TwigExtensionTest.php
@@ -32,7 +32,7 @@
       'autoescape' => TRUE,
       'optimizations' => 0
     ));
-    $twig->addExtension((new TwigExtension($renderer))->setGenerators($this->getMock('Drupal\Core\Routing\UrlGeneratorInterface'), $this->getMock('Drupal\Core\Theme\ThemeManagerInterface')));
+    $twig->addExtension((new TwigExtension($renderer))->setGenerators($this->getMock('Drupal\Core\Routing\UrlGeneratorInterface')));
 
     $nodes = $twig->parse($twig->tokenize($template));
 
@@ -78,7 +78,6 @@
   public function testActiveTheme() {
     $renderer = $this->getMock('\Drupal\Core\Render\RendererInterface');
     $extension = new TwigExtension($renderer);
-    $url_generator = $this->getMock('\Drupal\Core\Routing\UrlGeneratorInterface');
     $theme_manager = $this->getMock('\Drupal\Core\Theme\ThemeManagerInterface');
     $active_theme = $this->getMockBuilder('\Drupal\Core\Theme\ActiveTheme')
       ->disableOriginalConstructor()
@@ -91,7 +90,7 @@
       ->expects($this->once())
       ->method('getActiveTheme')
       ->willReturn($active_theme);
-    $extension->setGenerators($url_generator, $theme_manager);
+    $extension->setThemeManager($theme_manager);
 
     $loader = new \Twig_Loader_String();
     $twig = new \Twig_Environment($loader);