diff --git a/core/modules/block/migration_templates/d6_block.yml b/core/modules/block/migration_templates/d6_block.yml
index 8be7539..8a28a89 100644
--- a/core/modules/block/migration_templates/d6_block.yml
+++ b/core/modules/block/migration_templates/d6_block.yml
@@ -66,7 +66,10 @@ process:
       - region
       - theme
       - '@theme'
-    region_map:
+    # If the source and destination themes don't have the same regions,
+    # choose a region with static mapping. If no match is found in the
+    # map, the block will not be migrated at all.
+    map:
       left: sidebar_first
       right: sidebar_second
       sidebar_first: sidebar_first
diff --git a/core/modules/block/migration_templates/d7_block.yml b/core/modules/block/migration_templates/d7_block.yml
index ff56111..8d28432 100644
--- a/core/modules/block/migration_templates/d7_block.yml
+++ b/core/modules/block/migration_templates/d7_block.yml
@@ -70,7 +70,10 @@ process:
       - region
       - theme
       - '@theme'
-    region_map:
+    # If the source and destination themes don't have the same regions,
+    # choose a region with static mapping. If no match is found in the
+    # map, the block will not be migrated at all.
+    map:
       left: sidebar_first
       right: sidebar_second
       sidebar_first: sidebar_first
diff --git a/core/modules/block/src/Plugin/migrate/process/BlockRegion.php b/core/modules/block/src/Plugin/migrate/process/BlockRegion.php
index d05743e..26168fd 100644
--- a/core/modules/block/src/Plugin/migrate/process/BlockRegion.php
+++ b/core/modules/block/src/Plugin/migrate/process/BlockRegion.php
@@ -4,7 +4,7 @@
 
 use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
 use Drupal\migrate\MigrateExecutableInterface;
-use Drupal\migrate\ProcessPluginBase;
+use Drupal\migrate\Plugin\migrate\process\StaticMap;
 use Drupal\migrate\Row;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 
@@ -13,7 +13,7 @@
  *   id = "block_region"
  * )
  */
-class BlockRegion extends ProcessPluginBase implements ContainerFactoryPluginInterface {
+class BlockRegion extends StaticMap implements ContainerFactoryPluginInterface {
 
   /**
    * List of regions, keyed by theme.
@@ -66,15 +66,7 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
       }
     }
 
-    // If the source and destination theme are different, try to use the
-    // mappings defined in the configuration.
-    $region_map = $this->configuration['region_map'];
-    if (isset($region_map[$region])) {
-      return $region_map[$region];
-    }
-
-    // Oh well, we tried. Put the block in the main content region.
-    return 'content';
+    return parent::transform($value, $migrate_executable, $row, $destination_property);
   }
 
 }