diff --git a/xppbe/Post/Postcode.py b/xppbe/Post/Postcode.py
index 2e3142f..869c522 100644
--- a/xppbe/Post/Postcode.py
+++ b/xppbe/Post/Postcode.py
@@ -1074,7 +1074,9 @@ def plot_line_interface(self,N=1000, plot='u',value='phi', nn=np.array([0,1,0]))
     
     def save_values_file(self,save=True,L2_err_method='analytic_Born_Ion'):
 
-        L2_analytic = self.L2_interface_known('analytic_Born_Ion')
+        if L2_err_method is None:
+            L2_err_method = 'analytic_Born_Ion'
+        L2_analytic = self.L2_interface_known(L2_err_method)
         
         df_dict = super().save_values_file(save=False)
         df_dict['L2_analytic'] = '{:.3e}'.format(float(L2_analytic))