diff --git a/core/modules/migrate_drupal/src/Plugin/migrate/process/d6/BlockTheme.php b/core/modules/migrate_drupal/src/Plugin/migrate/process/d6/BlockTheme.php
index b6ea48f..ac27fe9 100644
--- a/core/modules/migrate_drupal/src/Plugin/migrate/process/d6/BlockTheme.php
+++ b/core/modules/migrate_drupal/src/Plugin/migrate/process/d6/BlockTheme.php
@@ -20,6 +20,7 @@
  * )
  */
 class BlockTheme extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+
   /**
    * Contains the configuration object factory.
    *
@@ -27,6 +28,13 @@ class BlockTheme extends ProcessPluginBase implements ContainerFactoryPluginInte
    */
   protected $configFactory;
 
+ /**
+  * Contains the system.theme configuration object.
+  *
+  * @var \Drupal\Core\Config\Config
+  */
+  protected $themeConfig;
+
   /**
    * Constructs a BlockTheme object.
    *
@@ -45,7 +53,7 @@ class BlockTheme extends ProcessPluginBase implements ContainerFactoryPluginInte
    */
   public function __construct(array $configuration, $plugin_id, $plugin_definition, MigrationInterface $migration, Config $theme_config, array $themes) {
     parent::__construct($configuration, $plugin_id, $plugin_definition, $migration);
-    $this->theme_config = $theme_config;
+    $this->themeConfig = $theme_config;
     $this->themes = $themes;
   }
 
@@ -77,8 +85,8 @@ public function transform($value, MigrateExecutable $migrate_executable, Row $ro
     }
 
     // Get the default destination themes.
-    $d8_default_theme = $this->theme_config->get('default');
-    $d8_admin_theme = $this->theme_config->get('admin');
+    $d8_default_theme = $this->themeConfig->get('default');
+    $d8_admin_theme = $this->themeConfig->get('admin');
 
     // If the source block is assigned to a region in the source default theme,
     // then assign it to the destination default theme.