diff --git a/msed/predict_events.py b/msed/predict_events.py
index 521d7ca..0c6f7aa 100644
--- a/msed/predict_events.py
+++ b/msed/predict_events.py
@@ -146,7 +146,7 @@ def predict_events(
                 for ev in window_events:
                     start = int(ev[0] * window_size) + window_idx * stride
                     stop = int(ev[1] * window_size) + window_idx * stride
-                    prediction_mask[ev[-1] - 1, start:stop] = 1
+                    prediction_mask[ev[-1], start:stop] = 1
             for ev, p in zip(class_names, prediction_mask):
                 predictions[subject_id][ev] = binary_to_array(p)
                 n_event = len(predictions[subject_id][ev])