diff --git a/examples/tmva/plot_multiclass.py b/examples/tmva/plot_multiclass.py
index 1191a82..ce42356 100644
--- a/examples/tmva/plot_multiclass.py
+++ b/examples/tmva/plot_multiclass.py
@@ -44,9 +44,10 @@
 # Call root_numpy's utility functions to add events from the arrays
 add_classification_events(factory, X_train, y_train, weights=w_train)
 add_classification_events(factory, X_test, y_test, weights=w_test, test=True)
+# The following line is necessary if events have been added individually:
+factory.PrepareTrainingAndTestTree(TCut('1'), 'NormMode=EqualNumEvents')
 
 # Train a BDT
-factory.PrepareTrainingAndTestTree(TCut('1'), 'NormMode=EqualNumEvents')
 factory.BookMethod('BDT', 'BDTG',
                    'nCuts=20:NTrees=20:MaxDepth=4:'
                    'BoostType=Grad:Shrinkage=0.10')
diff --git a/examples/tmva/plot_regression.py b/examples/tmva/plot_regression.py
index 59a820a..2007070 100644
--- a/examples/tmva/plot_regression.py
+++ b/examples/tmva/plot_regression.py
@@ -28,7 +28,9 @@
 
 add_regression_events(factory, X, y)
 add_regression_events(factory, X, y, test=True)
-factory.PrepareTrainingAndTestTree(TCut('1'), 'NormMode=EqualNumEvents')
+# The following line is necessary if events have been added individually:
+factory.PrepareTrainingAndTestTree(TCut('1'), '')
+
 factory.BookMethod('BDT', 'BDT1',
                    'nCuts=20:NTrees=1:MaxDepth=4:BoostType=AdaBoostR2:'
                    'SeparationType=RegressionVariance')
diff --git a/examples/tmva/plot_twoclass.py b/examples/tmva/plot_twoclass.py
index c4735ba..d92059d 100644
--- a/examples/tmva/plot_twoclass.py
+++ b/examples/tmva/plot_twoclass.py
@@ -42,9 +42,10 @@
 # Call root_numpy's utility functions to add events from the arrays
 add_classification_events(factory, X_train, y_train, weights=w_train)
 add_classification_events(factory, X_test, y_test, weights=w_test, test=True)
+# The following line is necessary if events have been added individually:
+factory.PrepareTrainingAndTestTree(TCut('1'), 'NormMode=EqualNumEvents')
 
 # Train a classifier
-factory.PrepareTrainingAndTestTree(TCut('1'), 'NormMode=EqualNumEvents')
 factory.BookMethod('Fisher', 'Fisher',
                    'Fisher:VarTransform=None:CreateMVAPdfs:'
                    'PDFInterpolMVAPdf=Spline2:NbinsMVAPdf=50:'