diff --git a/km3io/tools.py b/km3io/tools.py
index 27fa1d4e215aa63102ebd4427e5d9e69d29d6e71..2bc0e00ff99352e2d6f21663dd29771a00622076 100644
--- a/km3io/tools.py
+++ b/km3io/tools.py
@@ -276,7 +276,7 @@ def best_track(tracks, startend=None, minmax=None, stages=None):
 
     tracks = tracks[m1]
 
-    rec_stage_lengths = ak.num(tracks.rec_stages, axis=axis + 1)
+    rec_stage_lengths = ak.num(tracks.rec_stages, axis=-1)
     max_rec_stage_length = ak.max(rec_stage_lengths, axis=axis)
     m2 = rec_stage_lengths == max_rec_stage_length
     tracks = tracks[m2]