diff --git a/payroll/services/payroll.py b/payroll/services/payroll.py
index d0dc24c0..d6fe0936 100644
--- a/payroll/services/payroll.py
+++ b/payroll/services/payroll.py
@@ -76,14 +76,14 @@ def update_all_employee_pay_periods() -> None:
 
 class PayrollForecast(MonthsDict[int]):
     programme_code: str
-    natural_account_code: str
+    natural_account_code: int
 
 
 def payroll_forecast_report(
     cost_centre: CostCentre, financial_year: FinancialYear
 ) -> Iterator[PayrollForecast]:
     # { programme_code: { natural_account_code: np.array[ np.float64 ] } }
-    report: dict[str, dict[str, npt.NDArray[np.float64]]] = defaultdict(
+    report: dict[str, dict[int, npt.NDArray[np.float64]]] = defaultdict(
         lambda: defaultdict(lambda: np.zeros(12))
     )
 
diff --git a/payroll/tests/services/test_payroll.py b/payroll/tests/services/test_payroll.py
index 43c4bfd7..df658456 100644
--- a/payroll/tests/services/test_payroll.py
+++ b/payroll/tests/services/test_payroll.py
@@ -251,7 +251,7 @@ def test_scenario_update_forecast(db):
     financial_code_salary = FinancialCodeFactory(
         cost_centre=cost_centre,
         programme=programme_code,
-        natural_account_code__natural_account_code="71111001",
+        natural_account_code__natural_account_code=SALARY_NAC,
     )
 
     financial_year = FinancialYear.objects.current()
@@ -274,7 +274,7 @@ def test_scenario_update_forecast(db):
 
     payroll_forecast = PayrollForecast(
         programme_code=programme_code,
-        natural_account_code="71111001",
+        natural_account_code=SALARY_NAC,
         **expected_forecast,
     )