diff --git a/bitbylaw/steps/advoware_cal_sync/README.md b/bitbylaw/steps/advoware_cal_sync/README.md
index 3bca4763..63bafdb5 100644
--- a/bitbylaw/steps/advoware_cal_sync/README.md
+++ b/bitbylaw/steps/advoware_cal_sync/README.md
@@ -61,7 +61,7 @@ CREATE TABLE calendar_sync_audit (
 
 -- Indizes (angepasst für Soft Deletes)
 CREATE UNIQUE INDEX idx_calendar_sync_advoware ON calendar_sync (employee_kuerzel, advoware_frnr) WHERE advoware_frnr IS NOT NULL AND deleted = FALSE;
-CREATE UNIQUE INDEX idx_calendar_sync_google ON calendar_sync (employee_kuerzel, google_event_id) WHERE google_event_id IS NOT NULL;
+CREATE UNIQUE INDEX idx_calendar_sync_google ON calendar_sync (employee_kuerzel, google_event_id) WHERE google_event_id IS NOT NULL AND deleted = FALSE;
 ```
 
 ## Funktionalität
diff --git a/bitbylaw/steps/advoware_cal_sync/calendar_sync_event_step.py b/bitbylaw/steps/advoware_cal_sync/calendar_sync_event_step.py
index 861f53d9..115503d5 100644
--- a/bitbylaw/steps/advoware_cal_sync/calendar_sync_event_step.py
+++ b/bitbylaw/steps/advoware_cal_sync/calendar_sync_event_step.py
@@ -572,22 +572,37 @@ async def handler(event, context):
                     try:
                         if strategy == 'source_system_wins':
                             if row['source_system'] == 'advoware':
-                                # Check if Advoware was modified since last sync
+                                # Check for changes in source (Advoware) or unauthorized changes in target (Google)
                                 adv_ts = datetime.datetime.fromisoformat(adv_data['zuletztGeaendertAm']).astimezone(BERLIN_TZ)
+                                google_ts_str = google_data.get('updated', '')
+                                google_ts = datetime.datetime.fromisoformat(google_ts_str.rstrip('Z')).astimezone(BERLIN_TZ) if google_ts_str else None
                                 if adv_ts > row['last_sync']:
                                     await update_google_event(service, calendar_id, event_id, adv_std)
                                     async with conn.transaction():
                                         await conn.execute("UPDATE calendar_sync SET sync_status = 'synced', last_sync = $2 WHERE sync_id = $1;", row['sync_id'], adv_ts)
                                     logger.info(f"Phase 4: Updated Google event {event_id} from Advoware frNr {frnr}")
+                                elif google_ts and google_ts > row['last_sync']:
+                                    logger.warning(f"Phase 4: Unauthorized change in Google event {event_id}, resetting to Advoware frNr {frnr}")
+                                    await update_google_event(service, calendar_id, event_id, adv_std)
+                                    async with conn.transaction():
+                                        await conn.execute("UPDATE calendar_sync SET sync_status = 'synced', last_sync = $2 WHERE sync_id = $1;", row['sync_id'], adv_ts)
+                                    logger.info(f"Phase 4: Reset Google event {event_id} to Advoware frNr {frnr}")
                             elif row['source_system'] == 'google' and row['advoware_write_allowed']:
-                                # Check if Google was modified since last sync
+                                # Check for changes in source (Google) or unauthorized changes in target (Advoware)
                                 google_ts_str = google_data.get('updated', '')
                                 google_ts = datetime.datetime.fromisoformat(google_ts_str.rstrip('Z')).astimezone(BERLIN_TZ) if google_ts_str else None
+                                adv_ts = datetime.datetime.fromisoformat(adv_data['zuletztGeaendertAm']).astimezone(BERLIN_TZ)
                                 if google_ts and google_ts > row['last_sync']:
                                     await safe_update_advoware_appointment(advoware, frnr, google_std, row['advoware_write_allowed'])
                                     async with conn.transaction():
                                         await conn.execute("UPDATE calendar_sync SET sync_status = 'synced', last_sync = $2 WHERE sync_id = $1;", row['sync_id'], google_ts)
                                     logger.info(f"Phase 4: Updated Advoware frNr {frnr} from Google event {event_id}")
+                                elif adv_ts > row['last_sync']:
+                                    logger.warning(f"Phase 4: Unauthorized change in Advoware frNr {frnr}, resetting to Google event {event_id}")
+                                    await safe_update_advoware_appointment(advoware, frnr, google_std, row['advoware_write_allowed'])
+                                    async with conn.transaction():
+                                        await conn.execute("UPDATE calendar_sync SET sync_status = 'synced', last_sync = $2 WHERE sync_id = $1;", row['sync_id'], google_ts)
+                                    logger.info(f"Phase 4: Reset Advoware frNr {frnr} to Google event {event_id}")
                         elif strategy == 'last_change_wins':
                             adv_ts = await get_advoware_timestamp(advoware, frnr)
                             google_ts_str = google_data.get('updated', '')