diff -u b/core/core.services.yml b/core/core.services.yml
--- b/core/core.services.yml
+++ b/core/core.services.yml
@@ -1197,7 +1197,7 @@
     arguments: ['@app.root', '@theme_handler', '@state', '@module_handler']
   theme.registry:
     class: Drupal\Core\Theme\Registry
-    arguments: ['@app.root', '@cache.default', '@lock', '@module_handler', '@theme_handler', '@theme.initialization', '@request_stack']
+    arguments: ['@app.root', '@cache.default', '@lock', '@module_handler', '@theme_handler', '@theme.initialization']
     tags:
       - { name: needs_destruction }
     calls:
@@ -1208,7 +1208,7 @@
     arguments: ['@app.root', '@theme_handler', '@state', '@module_handler']
   theme.registry:
     class: Drupal\Core\Theme\Registry
-    arguments: ['@app.root', '@cache.default', '@lock', '@module_handler', '@theme_handler', '@theme.initialization']
+    arguments: ['@app.root', '@cache.default', '@lock', '@module_handler', '@theme_handler', '@theme.initialization', '@request_stack']
     tags:
       - { name: needs_destruction }
     calls:
diff -u b/core/lib/Drupal/Core/Utility/ThemeRegistry.php b/core/lib/Drupal/Core/Utility/ThemeRegistry.php
--- b/core/lib/Drupal/Core/Utility/ThemeRegistry.php
+++ b/core/lib/Drupal/Core/Utility/ThemeRegistry.php
@@ -82,11 +82,11 @@
   }
 
   /**
-   * Gets the persistable.
+   * Whether the partial registry can be persisted to the cache.
    *
    * @return bool
    */
-  protected function getPersistable() {
+  protected function isPersistable() {
     if ($this->persistable === NULL) {
       $this->persistable = $this->modulesLoaded && $this->requestStack->getCurrentRequest() !== NULL && $this->requestStack->getCurrentRequest()->isMethod('GET');
     }
@@ -101,7 +101,7 @@
    */
   protected function getStorage() {
     if (!$this->storage) {
-      if ($this->getPersistable() && $cached = $this->cache->get($this->getCid())) {
+      if ($this->isPersistable() && $cached = $this->cache->get($this->getCid())) {
         $this->storage = $cached->data;
       }
       else {
@@ -172,7 +172,7 @@
     }
     $storage = $this->getStorage();
     $storage[$key] = $this->completeRegistry[$key];
-    if ($this->getPersistable()) {
+    if ($this->isPersistable()) {
       $this->persist($key);
     }
     return $storage[$key];
@@ -182,7 +182,7 @@
    * {@inheritdoc}
    */
   protected function updateCache($lock = TRUE) {
-    if (!$this->getPersistable()) {
+    if (!$this->isPersistable()) {
       return;
     }
     // @todo: Is the custom implementation necessary?
diff -u b/core/modules/system/src/Tests/Theme/RegistryTest.php b/core/modules/system/src/Tests/Theme/RegistryTest.php
--- b/core/modules/system/src/Tests/Theme/RegistryTest.php
+++ b/core/modules/system/src/Tests/Theme/RegistryTest.php
@@ -73,12 +73,13 @@
   public function testMultipleSubThemes() {
     $theme_handler = \Drupal::service('theme_handler');
     $theme_handler->install(['test_basetheme', 'test_subtheme', 'test_subsubtheme']);
+    $request_stack = \Drupal::service('request_stack');
 
-    $registry_subsub_theme = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), 'test_subsubtheme');
+    $registry_subsub_theme = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), $request_stack, 'test_subsubtheme');
     $registry_subsub_theme->setThemeManager(\Drupal::theme());
-    $registry_sub_theme = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), 'test_subtheme');
+    $registry_sub_theme = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), $request_stack, 'test_subtheme');
     $registry_sub_theme->setThemeManager(\Drupal::theme());
-    $registry_base_theme = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), 'test_basetheme');
+    $registry_base_theme = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), $request_stack, 'test_basetheme');
     $registry_base_theme->setThemeManager(\Drupal::theme());
 
     $preprocess_functions = $registry_subsub_theme->get()['theme_test_template_test']['preprocess functions'];
@@ -113,7 +114,7 @@
     $theme_handler->install(['test_theme']);
     $theme_handler->setDefault('test_theme');
 
-    $registry = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), 'test_theme');
+    $registry = new Registry(\Drupal::root(), \Drupal::cache(), \Drupal::lock(), \Drupal::moduleHandler(), $theme_handler, \Drupal::service('theme.initialization'), \Drupal::service('request_stack'), 'test_theme');
     $registry->setThemeManager(\Drupal::theme());
     $this->assertEqual('value', $registry->get()['theme_test_template_test']['variables']['additional']);
   }
only in patch2:
unchanged:
--- a/core/tests/Drupal/Tests/Core/Theme/RegistryTest.php
+++ b/core/tests/Drupal/Tests/Core/Theme/RegistryTest.php
@@ -66,6 +66,8 @@ class RegistryTest extends UnitTestCase {
    */
   protected $themeManager;
 
+  protected $requestStack;
+
   /**
    * {@inheritdoc}
    */
@@ -78,6 +80,7 @@ protected function setUp() {
     $this->themeHandler = $this->getMock('Drupal\Core\Extension\ThemeHandlerInterface');
     $this->themeInitialization = $this->getMock('Drupal\Core\Theme\ThemeInitializationInterface');
     $this->themeManager = $this->getMock('Drupal\Core\Theme\ThemeManagerInterface');
+    $this->requestStack = $this->getMock('Symfony\Component\HttpFoundation\RequestStack');
 
     $this->setupTheme();
   }
@@ -131,7 +134,7 @@ public function testGetRegistryForModule() {
   }
 
   protected function setupTheme($theme_name = NULL) {
-    $this->registry = new TestRegistry($this->root, $this->cache, $this->lock, $this->moduleHandler, $this->themeHandler, $this->themeInitialization, $theme_name);
+    $this->registry = new TestRegistry($this->root, $this->cache, $this->lock, $this->moduleHandler, $this->themeHandler, $this->themeInitialization, $this->requestStack, $theme_name);
     $this->registry->setThemeManager($this->themeManager);
   }