diff --git a/dashboard/backend/routers/opc_tasks.py b/dashboard/backend/routers/opc_tasks.py
index b9f0b08..f099ce2 100644
--- a/dashboard/backend/routers/opc_tasks.py
+++ b/dashboard/backend/routers/opc_tasks.py
@@ -158,6 +158,12 @@ async def update_task(
     if new_status == "done" and old_status != "done":
         updates["completed_at"] = datetime.utcnow()
 
+    # Strip timezone info from datetime fields (database uses TIMESTAMP not TIMESTAMPTZ)
+    if "due_date" in updates and updates["due_date"] is not None:
+        updates["due_date"] = updates["due_date"].replace(tzinfo=None)
+    if "completed_at" in updates and updates["completed_at"] is not None:
+        updates["completed_at"] = updates["completed_at"].replace(tzinfo=None)
+
     updated_task = await opc_db.update_task(
         task_id=task_id,
         updates=updates,