diff --git a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
index 934c8b2..7737cc8 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -55,7 +55,6 @@
 
   private $moduleFiles;
   private $themeFiles;
-  private $themeData;
 
   /**
    * The configuration directories for this test run.
@@ -96,7 +95,6 @@ protected function beforePrepareEnvironment() {
     if (!isset($this->moduleFiles)) {
       $this->moduleFiles = \Drupal::state()->get('system.module.files') ?: array();
       $this->themeFiles = \Drupal::state()->get('system.theme.files') ?: array();
-      $this->themeData = \Drupal::state()->get('system.theme.data') ?: array();
     }
   }
 
@@ -139,7 +137,6 @@ protected function setUp() {
 
     \Drupal::state()->set('system.module.files', $this->moduleFiles);
     \Drupal::state()->set('system.theme.files', $this->themeFiles);
-    \Drupal::state()->set('system.theme.data', $this->themeData);
 
     // Bootstrap the kernel.
     // No need to dump it; this test runs in-memory.
diff --git a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
index 065d4c8..9f9217b 100644
--- a/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/TestBase.php
@@ -1015,10 +1015,6 @@ private function prepareEnvironment() {
     $this->originalContainer = clone \Drupal::getContainer();
     $this->originalLanguage = $language_interface;
     $this->originalConfigDirectories = $GLOBALS['config_directories'];
-    if (isset($GLOBALS['theme_key'])) {
-      $this->originalThemeKey = $GLOBALS['theme_key'];
-    }
-    $this->originalTheme = isset($GLOBALS['theme']) ? $GLOBALS['theme'] : NULL;
 
     // Save further contextual information.
     // Use the original files directory to avoid nesting it within an existing
@@ -1097,6 +1093,10 @@ private function prepareEnvironment() {
     unset($GLOBALS['conf']);
     unset($GLOBALS['theme_key']);
     unset($GLOBALS['theme']);
+    unset($GLOBALS['theme_info']);
+    unset($GLOBALS['base_theme_info']);
+    unset($GLOBALS['theme_engine']);
+    unset($GLOBALS['theme_path']);
 
     // Log fatal errors.
     ini_set('log_errors', 1);
@@ -1218,17 +1218,19 @@ private function restoreEnvironment() {
     $connection_info = Database::getConnectionInfo('default');
     $databases['default']['default'] = $connection_info['default'];
 
-    // Restore original globals.
-    if (isset($this->originalThemeKey)) {
-      $GLOBALS['theme_key'] = $this->originalThemeKey;
-    }
-    $GLOBALS['theme'] = $this->originalTheme;
-
     // Reset all static variables.
     // All destructors of statically cached objects have been invoked above;
     // this second reset is guaranteed to reset everything to nothing.
     drupal_static_reset();
 
+    // Reset global theme variables.
+    unset($GLOBALS['theme_key']);
+    unset($GLOBALS['theme']);
+    unset($GLOBALS['theme_info']);
+    unset($GLOBALS['base_theme_info']);
+    unset($GLOBALS['theme_engine']);
+    unset($GLOBALS['theme_path']);
+
     // Restore original in-memory configuration.
     $GLOBALS['config'] = $this->originalConfig;
     $GLOBALS['conf'] = $this->originalConf;