diff --git a/backend/app/routers/nextcloud.py b/backend/app/routers/nextcloud.py
index 552b1be..1461088 100644
--- a/backend/app/routers/nextcloud.py
+++ b/backend/app/routers/nextcloud.py
@@ -30,7 +30,7 @@ from typing import Optional
 
 from fastapi import APIRouter, Depends, HTTPException, Query
 from pydantic import BaseModel
-from sqlalchemy import delete, select
+from sqlalchemy import delete, select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.database import get_db
@@ -332,6 +332,17 @@ async def delete_nextcloud_source_root(
                 FolderShare.folder_type == 'folder',
             )
         )
+        # Folders have a self-referential parent_id FK with no
+        # ON DELETE rule. A flat DELETE of the whole subtree trips
+        # `folders_parent_id_fkey` because postgres checks the
+        # constraint per row, regardless of insertion / list order.
+        # NULL the parent_id on every folder we're about to delete
+        # first so the chain breaks cleanly.
+        await db.execute(
+            update(Folder)
+            .where(Folder.id.in_(folder_ids))
+            .values(parent_id=None)
+        )
         await db.execute(delete(Folder).where(Folder.id.in_(folder_ids)))
 
     await db.delete(sr)