diff --git a/km3io/offline.py b/km3io/offline.py
index 6f326516bc9216c8e0c93a6bafc9d9ed4bc5bb5e..4d67707f8b43742f06ca6fc4d6541d1a9dba5ef8 100644
--- a/km3io/offline.py
+++ b/km3io/offline.py
@@ -537,7 +537,7 @@ class OfflineReader:
 
             yield trk_index, stages_index
 
-    def _find_empty(self, chunk_arr):
+    def _find_empty(self, array):
         """finds empty lists/arrays in a chunked-jagged array of data
         of interest.