diff --git a/src/View/RegionViewBuilder.php b/src/View/RegionViewBuilder.php
index 4533012..7672985 100644
--- a/src/View/RegionViewBuilder.php
+++ b/src/View/RegionViewBuilder.php
@@ -8,6 +8,7 @@ use Drupal\Core\Config\ConfigFactoryInterface;
 use Drupal\Core\Controller\TitleResolverInterface;
 use Drupal\Core\Entity\EntityTypeManagerInterface;
 use Drupal\Core\Routing\RouteObjectInterface;
+use Drupal\Core\Theme\ThemeManagerInterface;
 use Symfony\Component\HttpFoundation\RequestStack;
 
 /**
@@ -43,6 +44,13 @@ class RegionViewBuilder {
    */
   protected $titleResolver;
 
+  /**
+   * The theme manager.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface
+   */
+  protected $themeManager;
+
   /**
    * Constructs a RegionViewBuilder object.
    */
@@ -50,12 +58,14 @@ 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 +81,9 @@ 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/tests/src/Kernel/RegionViewBuilderTest.php b/tests/src/Kernel/RegionViewBuilderTest.php
index 40a1eb8..e49316f 100644
--- a/tests/src/Kernel/RegionViewBuilderTest.php
+++ b/tests/src/Kernel/RegionViewBuilderTest.php
@@ -62,14 +62,14 @@ final class RegionViewBuilderTest extends AbstractTestCase {
 
     $build = $view_builder->build('sidebar_first');
     // The build should be empty because 'stark' is not a default theme.
-    $expected_build = [
+    $expected_sidebar_first = [
       '#cache' => [
         'contexts' => [],
         'tags' => ['config:block_list'],
         'max-age' => Cache::PERMANENT,
       ],
     ];
-    self::assertSame($expected_build, $build);
+    self::assertSame($expected_sidebar_first, $build);
 
     // Specify the theme name explicitly.
     $build = $view_builder->build('sidebar_first', 'stark');
@@ -137,7 +137,7 @@ final class RegionViewBuilderTest extends AbstractTestCase {
       ->save();
 
     $build = $view_builder->build('sidebar_first');
-    self::assertRenderArray($expected_build, $build);
+    self::assertRenderArray($expected_sidebar_first, $build);
 
     Html::resetSeenIds();
     $actual_html = $renderer->renderPlain($expected_build);
diff --git a/twig_tweak.services.yml b/twig_tweak.services.yml
index b224788..c0f2839 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