diff --git a/backend/magic_plan/magic_plan_service.py b/backend/magic_plan/magic_plan_service.py
index 2be3379d..8a75c716 100644
--- a/backend/magic_plan/magic_plan_service.py
+++ b/backend/magic_plan/magic_plan_service.py
@@ -1,7 +1,7 @@
 import gzip
 import json
 from datetime import datetime, timezone
-from typing import Optional
+from typing import Optional, cast
 
 from datatypes.magicplan.api.response import MagicPlanPlan, PlanSummary
 from datatypes.magicplan.domain.mapper import map_plan
@@ -57,7 +57,7 @@ class MagicPlanService:
         with db_session() as session:
             session.add(uploaded_file)
             session.flush()
-            save_plan(session, plan, uploaded_file.id)
+            save_plan(session, plan, cast(int, uploaded_file.id))
 
         return plan
 
diff --git a/backend/magic_plan/tests/test_magic_plan_service.py b/backend/magic_plan/tests/test_magic_plan_service.py
index 158cf4d6..a2302ab4 100644
--- a/backend/magic_plan/tests/test_magic_plan_service.py
+++ b/backend/magic_plan/tests/test_magic_plan_service.py
@@ -271,3 +271,38 @@ def test_run_creates_uploaded_file_record(
     assert uploaded_file.s3_upload_timestamp is not None
     assert uploaded_file.uprn == 100023336956
     assert uploaded_file.hubspot_deal_id == "deal-789"
+
+
+def test_run_passes_flushed_uploaded_file_id_to_save_plan(
+    mock_client: MagicMock,
+    plan_summary: PlanSummary,
+) -> None:
+    # Arrange
+    mock_client.get_plans.return_value = [plan_summary]
+    service = _make_service(mock_client)
+    mock_session = MagicMock()
+    added_objects: list = []
+
+    mock_session.add.side_effect = added_objects.append
+
+    def simulate_flush() -> None:
+        for obj in added_objects:
+            if isinstance(obj, UploadedFile):
+                obj.id = 42
+
+    mock_session.flush.side_effect = simulate_flush
+
+    with patch(
+        "backend.magic_plan.magic_plan_service.find_matching_plan",
+        return_value=plan_summary,
+    ), patch("backend.magic_plan.magic_plan_service.save_plan") as mock_save, patch(
+        "backend.magic_plan.magic_plan_service.db_session"
+    ) as mock_db, patch(
+        "backend.magic_plan.magic_plan_service.save_data_to_s3"
+    ):
+        mock_db.return_value.__enter__.return_value = mock_session
+        # Act
+        service.run(_make_request())
+
+    # Assert
+    assert mock_save.call_args[0][2] == 42