diff --git a/nmreval/fit/parameter.py b/nmreval/fit/parameter.py
index 12f92ed..cc18c85 100644
--- a/nmreval/fit/parameter.py
+++ b/nmreval/fit/parameter.py
@@ -118,7 +118,7 @@ class Parameter:
             return start + f'{self.value:} (fixed)'
 
     def __add__(self, other: Parameter | float) -> float:
-        if isinstance(other, float):
+        if isinstance(other, (float, int)):
             return self.value + other
         elif isinstance(other, Parameter):
             return self.value + other.value
diff --git a/nmreval/gui_qt/data/datawidget/datawidget.py b/nmreval/gui_qt/data/datawidget/datawidget.py
index 68b5ec3..ddc8fcb 100644
--- a/nmreval/gui_qt/data/datawidget/datawidget.py
+++ b/nmreval/gui_qt/data/datawidget/datawidget.py
@@ -1,4 +1,4 @@
-from typing import List, Union
+from typing import List, Tuple, Union
 
 from .properties import PropWidget
 from ...Qt import QtWidgets, QtGui, QtCore
@@ -77,7 +77,7 @@ class DataTree(QtWidgets.QTreeWidget):
                 break
 
     @QtCore.pyqtSlot(QtWidgets.QTreeWidgetItem)
-    def data_change(self, item: QtWidgets.QTreeWidgetItem) -> tuple[set, set]:
+    def data_change(self, item: QtWidgets.QTreeWidgetItem) -> Tuple[set, set]:
         idd = item.data(0, QtCore.Qt.UserRole)
         is_selected = item.checkState(0) == QtCore.Qt.Checked
         to_be_hidden = set()
diff --git a/nmreval/gui_qt/fit/fitwindow.py b/nmreval/gui_qt/fit/fitwindow.py
index 320e83b..cff9c8e 100644
--- a/nmreval/gui_qt/fit/fitwindow.py
+++ b/nmreval/gui_qt/fit/fitwindow.py
@@ -443,7 +443,7 @@ class QFitDialog(QtWidgets.QWidget, Ui_FitDialog):
 
                     self.set_parameter_iter(fit_id, [p.value for p in fit_parameter], self.models[fitted_model])
 
-            mean_parameter = [reduce(add, p)/len(p) for p in zip(*glob_fit_parameter)]
+            mean_parameter = [reduce(add, p, 0)/len(p) for p in zip(*glob_fit_parameter)]
 
             self.set_parameter_iter(None, mean_parameter, self.models[fitted_model])