diff --git a/ctapipe/tools/train_particle_classifier.py b/ctapipe/tools/train_particle_classifier.py
index 90324b5d5b8..70c53b63419 100644
--- a/ctapipe/tools/train_particle_classifier.py
+++ b/ctapipe/tools/train_particle_classifier.py
@@ -193,7 +193,7 @@ def _read_input_data(self, tel_type):
             feature_names=feature_names,
             rng=self.rng,
             log=self.log,
-            n_events=self.n_signal.tel[tel_type],
+            n_events=self.n_background.tel[tel_type],
         )
         table = vstack([signal, background])
         self.log.info(