diff --git a/includes/functions.php b/includes/functions.php
index fea1821..0fd9276 100644
--- a/includes/functions.php
+++ b/includes/functions.php
@@ -2,6 +2,7 @@
 namespace Activitypub;
 
 use WP_Error;
+use WP_Comment_Query;
 use Activitypub\Http;
 use Activitypub\Activity\Activity;
 use Activitypub\Collection\Followers;
@@ -622,3 +623,29 @@ function get_total_users() {
 
 	return $users + 1;
 }
+
+/**
+ * Examine a comment ID and look up an existing comment it represents.
+ *
+ * @param string $id ActivityPub object ID (usually a URL) to check.
+ *
+ * @return int|boolean Comment ID, or false on failure.
+ */
+function object_id_to_comment( $id ) {
+	$comment_query = new WP_Comment_Query(
+		array(
+			'meta_key'   => 'source_id', // phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_meta_key
+			'meta_value' => $id,         // phpcs:ignore WordPress.DB.SlowDBQuery.slow_db_query_meta_value
+		)
+	);
+
+	if ( ! $comment_query->comments ) {
+		return false;
+	}
+
+	if ( count( $comment_query->comments ) > 1 ) {
+		return false;
+	}
+
+	return $comment_query->comments[0];
+}
diff --git a/includes/handler/class-delete.php b/includes/handler/class-delete.php
index d4530c9..a33ffdd 100644
--- a/includes/handler/class-delete.php
+++ b/includes/handler/class-delete.php
@@ -21,7 +21,11 @@ class Delete {
 	 * @param int   $user_id  The ID of the user performing the delete activity.
 	 */
 	public function handle_delete( $activity, $user_id ) {
-		if ( ! isset( $activity['object'] ) || ! is_array( $activity['object'] ) ) {
+		if (
+			! isset( $activity['object'] ) ||
+			! is_array( $activity['object'] ) ||
+			! isset( $activity['object']['id'] )
+		) {
 			return;
 		}
 
@@ -33,7 +37,10 @@ class Delete {
 			case 'Organization':
 			case 'Service':
 			case 'Application':
-				Followers::remove_follower( $activity['object']['id'], $user_id );
+				$follower = Followers::get_follower( $user_id, $activity['actor'] );
+				if ( $follower ) {
+					$follower->delete();
+				}
 
 				break;
 			case 'Tombstone':
diff --git a/includes/handler/class-undo.php b/includes/handler/class-undo.php
index 9c68924..7d39868 100644
--- a/includes/handler/class-undo.php
+++ b/includes/handler/class-undo.php
@@ -23,6 +23,7 @@ class Undo {
 	public static function handle_undo( $activity, $user_id ) {
 		if (
 			isset( $activity['object'] ) &&
+			isset( $activity['actor'] ) &&
 			isset( $activity['object']['type'] ) &&
 			'Follow' === $activity['object']['type']
 		) {