diff --git a/qlayers/tests/test_thickness.py b/qlayers/tests/test_thickness.py
index 449c027..c1dfa45 100644
--- a/qlayers/tests/test_thickness.py
+++ b/qlayers/tests/test_thickness.py
@@ -159,5 +159,6 @@ def get_df(self, _):
                 return df_wide
 
         thickness, thickness_err = cortical_thickness(MockQLayers(), est_error=True)
-        assert np.isclose(thickness, 8.98140)
-        assert np.isclose(thickness_err, 5.28871)
+
+        assert np.isclose(thickness, 8.53326)
+        assert np.isclose(thickness_err, 4.72645)
diff --git a/qlayers/thickness.py b/qlayers/thickness.py
index e9c3b88..9f9ef38 100644
--- a/qlayers/thickness.py
+++ b/qlayers/thickness.py
@@ -3,6 +3,8 @@
 from scipy import stats
 from scipy.optimize import curve_fit, fsolve
 
+np.random.seed(0)
+
 
 def logistic(x, L, x0, k):
     """