diff --git a/activitypub.php b/activitypub.php
index 380b438..bf718f2 100644
--- a/activitypub.php
+++ b/activitypub.php
@@ -33,12 +33,15 @@ require_once __DIR__ . '/includes/functions.php';
 \defined( 'ACTIVITYPUB_CUSTOM_POST_CONTENT' ) || \define( 'ACTIVITYPUB_CUSTOM_POST_CONTENT', "<strong>[ap_title]</strong>\n\n[ap_content]\n\n[ap_hashtags]\n\n[ap_shortlink]" );
 \defined( 'ACTIVITYPUB_AUTHORIZED_FETCH' ) || \define( 'ACTIVITYPUB_AUTHORIZED_FETCH', false );
 \defined( 'ACTIVITYPUB_DISABLE_REWRITES' ) || \define( 'ACTIVITYPUB_DISABLE_REWRITES', false );
+\defined( 'ACTIVITYPUB_DEFAULT_TRANSFORMER' ) || \define( 'ACTIVITYPUB_DEFAULT_TRANSFORMER', 'activitypub/defualt' );
+
 
 \define( 'ACTIVITYPUB_PLUGIN_DIR', plugin_dir_path( __FILE__ ) );
 \define( 'ACTIVITYPUB_PLUGIN_BASENAME', plugin_basename( __FILE__ ) );
 \define( 'ACTIVITYPUB_PLUGIN_FILE', plugin_dir_path( __FILE__ ) . '/' . basename( __FILE__ ) );
 \define( 'ACTIVITYPUB_PLUGIN_URL', plugin_dir_url( __FILE__ ) );
 
+
 /**
  * Initialize REST routes.
  */
diff --git a/includes/class-migration.php b/includes/class-migration.php
index cd13f8d..74ecfbe 100644
--- a/includes/class-migration.php
+++ b/includes/class-migration.php
@@ -4,6 +4,7 @@ namespace Activitypub;
 use Activitypub\Activitypub;
 use Activitypub\Model\Blog_User;
 use Activitypub\Collection\Followers;
+use Activitypub\Admin;
 
 /**
  * ActivityPub Migration Class
@@ -114,12 +115,30 @@ class Migration {
 		if ( version_compare( $version_from_db, '1.0.0', '<' ) ) {
 			self::migrate_from_0_17();
 		}
+		if ( version_compare( $version_from_db, 'version_number_transformer_management_placeholder', '<' ) ) {
+			self::migrate_from_version_number_transformer_management_placeholder();
+		}
 
 		update_option( 'activitypub_db_version', self::get_target_version() );
 
 		self::unlock();
 	}
 
+	/**
+	 * Updates the supported post type settings to the mapped transformer setting.
+	 * TODO: Test this
+	 * @return void
+	 */
+	private static function migrate_from_version_number_transformer_management_placeholder() {
+		$supported_post_types = \get_option( 'activitypub_support_post_types', array( 'post', 'page' ) );
+		Admin::register_settings();
+		$transformer_mapping = array();
+		foreach ( $supported_post_types as $supported_post_type ) {
+			$transformer_mapping[ $supported_post_type ] = ACTIVITYPUB_DEFAULT_TRANSFORMER;
+		}
+		update_option( 'activitypub_transformer_mapping', $transformer_mapping );
+	}
+
 	/**
 	 * Updates the DB-schema of the followers-list
 	 *
diff --git a/includes/class-transformers-manager.php b/includes/class-transformers-manager.php
index dc425e5..a546a4a 100644
--- a/includes/class-transformers-manager.php
+++ b/includes/class-transformers-manager.php
@@ -28,8 +28,8 @@ if ( ! defined( 'ABSPATH' ) ) {
 
 class Transformers_Manager {
 	const DEFAULT_TRANSFORMER_MAPPING = array(
-		'post' => 'activitypub/default',
-		'page' => 'activitypub/default'
+		'post' => ACTIVITYPUB_DEFAULT_TRANSFORMER,
+		'page' => ACTIVITYPUB_DEFAULT_TRANSFORMER,
 	);
 
 	/**