diff --git a/src/nmreval/fit/result.py b/src/nmreval/fit/result.py
index 37d513f..27b293b 100644
--- a/src/nmreval/fit/result.py
+++ b/src/nmreval/fit/result.py
@@ -393,8 +393,7 @@ class FitResult(Points):
     def get_state(self):
         state = super().get_state()
 
-        for attr in ['idx', 'fun_kwargs', 'nobs', 'nvar',
-                     'islog', 'iscomplex', 'x_data', 'y_data']:
+        for attr in ['idx', 'fun_kwargs', 'nobs', 'nvar', 'we', 'islog', 'iscomplex', 'x_data', 'y_data']:
             state[attr] = getattr(self, attr)
 
         state['name'] = self._model_name
@@ -412,6 +411,8 @@ class FitResult(Points):
     @staticmethod
     def set_state(state, **kwargs):
         state['params'] = {k: Parameter.set_state(v) for k, v in state.pop('params').items()}
+        if 'we' not in state:
+            state['we'] = '?'
         data = FitResult(**state)
 
         return data
@@ -440,6 +441,9 @@ class FitResult(Points):
         return new_fit
 
     def sub(self, x_values):
+        if self.func is None:
+            raise ValueError('no fit function available to calculate new y values')
+
         part_functions = []
         actual_mode = -1
         if 'complex_mode' in self.fun_kwargs: