diff --git a/scripts/checkTrackSelection.py b/scripts/checkTrackSelection.py
index 9fe079e..2daab24 100644
--- a/scripts/checkTrackSelection.py
+++ b/scripts/checkTrackSelection.py
@@ -3,7 +3,7 @@
 # @Author: Elena Graverini
 # @Date:   2015-10-27 18:26:49
 # @Last Modified by:   Elena Graverini
-# @Last Modified time: 2017-05-22 16:54:29
+# @Last Modified time: 2017-05-22 16:59:06
 import sys
 import os
 from math import sqrt
@@ -256,7 +256,8 @@
 
 
 def myTFunc(name, classname, func, func_range, par_names, par_inits=[], par_limits=[]):
-    f = r.__getattr__(classname)(name, MyFitFunction(func), *func_range)
+    n_pars = len(par_names)
+    f = r.__getattr__(classname)(name, MyFitFunction(func), *func_range, n_pars)
     f.SetParNames(*par_names)
     if par_inits:
         f.SetParameters(*par_inits)