diff --git a/src/View/RegionViewBuilder.php b/src/View/RegionViewBuilder.php
index 4533012..5ebbb01 100644
--- a/src/View/RegionViewBuilder.php
+++ b/src/View/RegionViewBuilder.php
@@ -7,7 +7,9 @@ use Drupal\Core\Cache\CacheableMetadata;
 use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Controller\TitleResolverInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Extension\ThemeHandlerInterface;
 use Drupal\Core\Routing\RouteObjectInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
@@ -43,6 +45,13 @@ class RegionViewBuilder {
    */
   protected $titleResolver;
 
+  /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
   /**
    * Constructs a RegionViewBuilder object.
    */
@@ -50,12 +59,14 @@ class RegionViewBuilder {
     EntityTypeManagerInterface $entity_type_manager,
     ConfigFactoryInterface $config_factory,
     RequestStack $request_stack,
-    TitleResolverInterface $title_resolver
+    TitleResolverInterface $title_resolver,
+    ThemeManagerInterface $theme_manager
   ) {
     $this->entityTypeManager = $entity_type_manager;
     $this->configFactory = $config_factory;
     $this->requestStack = $request_stack;
     $this->titleResolver = $title_resolver;
+    $this->themeManager = $theme_manager;
   }
 
   /**
@@ -71,10 +82,9 @@ class RegionViewBuilder {
    *   A render array to display the region content.
    */
   public function build(string $region, string $theme = NULL): array {
-
     $blocks = $this->entityTypeManager->getStorage('block')->loadByProperties([
       'region' => $region,
-      'theme'  => $theme ?: $this->configFactory->get('system.theme')->get('default'),
+      'theme'  => $theme ?: $this->themeManager->getActiveTheme()->getName(),
     ]);
 
     $view_builder = $this->entityTypeManager->getViewBuilder('block');
diff --git a/twig_tweak.services.yml b/twig_tweak.services.yml
index f5c6ef3..5f47fb1 100644
--- a/twig_tweak.services.yml
+++ b/twig_tweak.services.yml
@@ -11,7 +11,7 @@ services:
 
   twig_tweak.region_view_builder:
     class: Drupal\twig_tweak\View\RegionViewBuilder
-    arguments: ['@entity_type.manager', '@config.factory', '@request_stack', '@title_resolver']
+    arguments: ['@entity_type.manager', '@config.factory', '@request_stack', '@title_resolver', '@theme.manager']
 
   twig_tweak.entity_view_builder:
     class: Drupal\twig_tweak\View\EntityViewBuilder