diff --git a/toolkit.py b/toolkit.py
index 3e75d2ccd65697af669af7016abf7905bfb769ac..67804358efbb463f23134d8bafa5f2205b01cb1a 100755
--- a/toolkit.py
+++ b/toolkit.py
@@ -1024,7 +1024,9 @@ class ClassificationProject(object):
     def write_friend_tree(self, score_name,
                           source_filename, source_treename,
                           target_filename, target_treename,
-                          batch_size=100000, score_mode=None):
+                          batch_size=100000,
+                          score_mode=None,
+                          fixed_params=None):
         f = ROOT.TFile.Open(source_filename)
         tree = f.Get(source_treename)
         entries = tree.GetEntries()
@@ -1037,8 +1039,11 @@ class ClassificationProject(object):
             x_from_tree = tree2array(tree,
                                      branches=self.branches+self.identifiers,
                                      start=start, stop=start+batch_size)
+            # for parametrized classifiers
+            if fixed_params is not None:
+                for param_name, value in fixed_params.items():
+                    x_from_tree[param_name] = value
             x_eval = rec2array(x_from_tree[self.branches])
-
             if len(self.identifiers) > 0:
                 # create list of booleans that indicate which events where used for training
                 df_identifiers = pd.DataFrame(x_from_tree[self.identifiers])