diff --git a/files/acp/be.bastelstu.chat_update_deleteOrphanedAttachments.php b/files/acp/be.bastelstu.chat_update_deleteOrphanedAttachments.php
new file mode 100644
index 0000000..24373fb
--- /dev/null
+++ b/files/acp/be.bastelstu.chat_update_deleteOrphanedAttachments.php
@@ -0,0 +1,41 @@
+<?php
+
+/**
+ * Deletes orphaned attachments.
+ *
+ * @author  Tim Duesterhus
+ * @copyright   2001-2022 WoltLab GmbH
+ * @license GNU Lesser General Public License <http://opensource.org/licenses/lgpl-license.php>
+ * @package WoltLabSuite\Core
+ * @see https://github.com/WoltLab/com.woltlab.wcf.conversation/blob/f0d4964a0b8042c440d5a3f759078429dc43c5b8/files/acp/update_com.woltlab.wcf.conversation_5.5_cleanup_orphaned_attachments.php
+ */
+
+use wcf\data\attachment\AttachmentAction;
+use wcf\data\object\type\ObjectTypeCache;
+use wcf\system\package\SplitNodeException;
+use wcf\system\WCF;
+
+$objectType = ObjectTypeCache::getInstance()
+    ->getObjectTypeByName('com.woltlab.wcf.attachment.objectType', 'be.bastelstu.chat.message');
+
+$sql = "SELECT  attachmentID
+        FROM    wcf1_attachment
+        WHERE   objectTypeID = ?
+            AND objectID NOT IN (
+                SELECT  messageID
+                FROM    chat1_message
+            )";
+$statement = WCF::getDB()->prepare($sql, 100);
+$statement->execute([$objectType->objectTypeID]);
+$attachmentIDs = $statement->fetchAll(\PDO::FETCH_COLUMN);
+
+if (empty($attachmentIDs)) {
+    return;
+}
+
+(new AttachmentAction($attachmentIDs, 'delete'))->executeAction();
+
+// If we reached this location we processed at least one attachment.
+// If this was the final attachment the next iteration will abort this
+// script early, thus not splitting the node.
+throw new SplitNodeException();