diff --git a/backend/services/planning_engine.py b/backend/services/planning_engine.py
index 7b2be3c..0bb1db3 100644
--- a/backend/services/planning_engine.py
+++ b/backend/services/planning_engine.py
@@ -229,9 +229,12 @@ async def compute_correction_factor(
     )
     j = raw if isinstance(raw, dict) else json.loads(raw)
     factor = float(j.get("correction_factor", 1.0))
+    # JSON z DB má často ISO řetězce; asyncpg u $2/$3 vyžaduje datetime
+    ws = _parse_json_dt(j.get("window_start")) or window_start
+    we = _parse_json_dt(j.get("window_end")) or now
     log_data = {
-        "window_start": j.get("window_start", window_start),
-        "window_end": j.get("window_end", now),
+        "window_start": ws,
+        "window_end": we,
         "actual_pv_wh": j.get("actual_pv_wh"),
         "forecast_pv_wh": j.get("forecast_pv_wh"),
         "correction_factor": factor,