diff --git a/src/gui_qt/fit/fitwindow.py b/src/gui_qt/fit/fitwindow.py
index a5a4fd0..443e894 100644
--- a/src/gui_qt/fit/fitwindow.py
+++ b/src/gui_qt/fit/fitwindow.py
@@ -495,7 +495,7 @@ class QFitDialog(QtWidgets.QWidget, Ui_FitDialog):
             if model_p['active']:
                 cnt += self.param_widgets[model_p['cnt']].set_parameter(fit_id, param[cnt:])
                 if model_p['children']:
-                    cnt += self.set_parameter_iter(fit_id, param, model_p['children'], cnt=cnt)
+                    cnt = self.set_parameter_iter(fit_id, param, model_p['children'], cnt=cnt)
 
         return cnt