diff --git a/backend/app/routers/photos.py b/backend/app/routers/photos.py
index 9c76500..aecc977 100644
--- a/backend/app/routers/photos.py
+++ b/backend/app/routers/photos.py
@@ -2,7 +2,7 @@
 Photos API router
 """
 from typing import List, Optional, Dict, Any
-from datetime import datetime
+from datetime import datetime, timezone
 from pathlib import Path
 from fastapi import APIRouter, Depends, HTTPException, Query, Response
 from fastapi.responses import FileResponse
@@ -888,6 +888,15 @@ async def update_photo(
     if 'taken_at' in update_data:
         new_dt = update_data.pop('taken_at')
         if new_dt is not None:
+            # The frontend's <input type="datetime-local"> usually serializes
+            # without a tz, but a manual edit / paste / certain locales can
+            # send a tz-aware ISO (e.g. "2026-05-09T00:12+02:00"). The
+            # photos.taken_at column is `timestamp without time zone`, so
+            # asyncpg can't bind a tz-aware value — it raises
+            # "can't subtract offset-naive and offset-aware datetimes".
+            # Normalize to naive UTC so both shapes round-trip cleanly.
+            if new_dt.tzinfo is not None:
+                new_dt = new_dt.astimezone(timezone.utc).replace(tzinfo=None)
             try:
                 await write_taken_at(photo.filepath, new_dt)
             except ExifWriteError as exc: