diff --git a/src/nmreval/data/points.py b/src/nmreval/data/points.py
index cd3553a..bf9a438 100644
--- a/src/nmreval/data/points.py
+++ b/src/nmreval/data/points.py
@@ -484,7 +484,7 @@ class Points:
 
         return self
 
-    def set_data(self, x: np.ndarray = None, y: np.ndarray = None, y_err: np.ndarray = None, replace_mask=True) -> PointLike:
+    def set_data(self, x: np.ndarray = None, y: np.ndarray = None, y_err: np.ndarray | float = None, replace_mask: bool = True) -> PointLike:
         if x is None:
             x = self._x
         if y is None:
diff --git a/src/nmreval/fit/result.py b/src/nmreval/fit/result.py
index 65d340d..4d98cd8 100644
--- a/src/nmreval/fit/result.py
+++ b/src/nmreval/fit/result.py
@@ -387,7 +387,7 @@ class FitResult(Points):
 
             self.fun_kwargs['complex_mode'] = actual_mode
 
-        new_fit.set_data(x_values, y_values)
+        new_fit.set_data(x_values, y_values, y_err=0.0)
 
         return new_fit
 
@@ -410,7 +410,7 @@ class FitResult(Points):
             else:
                 part_functions.append(Points(x_values, sub_y, name=sub_name))
 
-        if actual_mode < 0:
+        if actual_mode > 0:
             self.fun_kwargs['complex_mode'] = actual_mode
 
         return part_functions