diff --git a/toolkit.py b/toolkit.py
index 0bc2c2918098b2857c657110ba73893501942f0e..7e1954a2bd89e6b1eece8f42508c7371de156202 100755
--- a/toolkit.py
+++ b/toolkit.py
@@ -283,8 +283,8 @@ class ClassificationProject(object):
                                      selection=self.selection,
                                      start=1, step=self.step_bkg)
 
-            self.s_eventlist_train = self.s_train[self.identifiers]
-            self.b_eventlist_train = self.b_train[self.identifiers]
+            self.s_eventlist_train = self.s_train[self.identifiers].astype(dtype=[(branchName, "u8") for branchName in self.identifiers])
+            self.b_eventlist_train = self.b_train[self.identifiers].astype(dtype=[(branchName, "u8") for branchName in self.identifiers])
             self._dump_training_list()
 
             # now we don't need the identifiers anymore