diff --git a/core/core.services.yml b/core/core.services.yml
index 10cd1e5..1221071 100644
--- a/core/core.services.yml
+++ b/core/core.services.yml
@@ -662,7 +662,7 @@ services:
     class: Zend\Feed\Writer\Extension\Threading\Renderer\Entry
   feed.writer.wellformedwebrendererentry:
     class: Zend\Feed\Writer\Extension\WellFormedWeb\Renderer\Entry
-  theme.initialisation:
+  theme.initialization:
     class: Drupal\Core\Theme\Initialization
     arguments: ['@theme_handler', '@theme.negotiator']
     calls:
diff --git a/core/includes/install.core.inc b/core/includes/install.core.inc
index c3aea66..50a1d45 100644
--- a/core/includes/install.core.inc
+++ b/core/includes/install.core.inc
@@ -418,7 +418,7 @@ function install_begin_request(&$install_state) {
       ->addTag('needs_destruction');
 
     $container
-      ->register('theme.initialisation', 'Drupal\Core\Theme\Initialisation')
+      ->register('theme.initialization', 'Drupal\Core\Theme\Initialization')
       ->addArgument(new Reference('theme_handler'))
       ->addArgument(new Reference('theme.negotiator'));
     $container
diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 8d1999d..0c77a4c 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -84,7 +84,7 @@ function drupal_theme_access($theme) {
  * Initializes the theme system by loading the theme.
  */
 function drupal_theme_initialize() {
-  \Drupal::service('theme.initialisation')->initThemeSystem();
+  \Drupal::service('theme.initialization')->initThemeSystem();
 }
 
 /**
diff --git a/core/includes/theme.maintenance.inc b/core/includes/theme.maintenance.inc
index e5826e3..4e2a011 100644
--- a/core/includes/theme.maintenance.inc
+++ b/core/includes/theme.maintenance.inc
@@ -90,8 +90,7 @@ function _drupal_maintenance_theme() {
     $base_theme[] = $new_base_theme = $themes[$themes[$ancestor]->base_theme];
     $ancestor = $themes[$ancestor]->base_theme;
   }
-  \Drupal::service('theme.initialisation')->addAssets($themes[$theme], array_reverse($base_theme));
-  \Drupal::service('theme.initialisation')->loadIncludes($themes[$theme], array_reverse($base_theme));
+  \Drupal::service('theme.initialization')->initThemeSystemWithLoadedInformation($themes[$theme], array_reverse($base_theme));
   // Prime the theme registry.
   // @todo Remove global theme variables.
   Drupal::service('theme.registry');