diff --git a/factor_attribution.py b/factor_attribution.py
index ee90b95..03d42f2 100644
--- a/factor_attribution.py
+++ b/factor_attribution.py
@@ -308,6 +308,8 @@ def run_factor_regression(
 
     fitted = x @ coefficients
     residuals = y.to_numpy() - fitted
+    residual_series = pd.Series(residuals, index=regression_frame.index)
+    residual_vol_ann = float(residual_series.std(ddof=1) * np.sqrt(TRADING_DAYS_PER_YEAR))
 
     dof = n_obs - param_count
     if dof > 0:
@@ -323,12 +325,10 @@ def run_factor_regression(
                 where=standard_errors > 0,
             )
         p_values = 2.0 * stats.t.sf(np.abs(t_stats), df=dof)
-        residual_vol_ann = float(pd.Series(residuals, index=regression_frame.index).std(ddof=1) * np.sqrt(TRADING_DAYS_PER_YEAR))
         adj_r_squared_is_defined = True
     else:
         t_stats = np.full_like(coefficients, np.nan, dtype=float)
         p_values = np.full_like(coefficients, np.nan, dtype=float)
-        residual_vol_ann = float("nan")
         adj_r_squared_is_defined = False
 
     ss_total = float(((y - y.mean()) ** 2).sum())
diff --git a/tests/test_factor_attribution.py b/tests/test_factor_attribution.py
index e615c0b..9b369db 100644
--- a/tests/test_factor_attribution.py
+++ b/tests/test_factor_attribution.py
@@ -499,7 +499,7 @@ class RegressionTests(unittest.TestCase):
         self.assertTrue(np.isnan(result["p_values"]["MKT_RF"]))
         self.assertTrue(np.isnan(result["p_values"]["SMB"]))
         self.assertTrue(np.isnan(result["adj_r_squared"]))
-        self.assertTrue(np.isnan(result["residual_vol_ann"]))
+        self.assertAlmostEqual(result["residual_vol_ann"], 0.0, places=12)
 
     def test_run_factor_regression_rejects_rank_deficient_designs(self):
         dates = pd.date_range("2024-01-01", periods=6, freq="B")