diff --git a/km3io/tools.py b/km3io/tools.py
index 67d2c7415e2666702fcff5b72892670d43cd1195..b9c98efce82b9c913443492b79d9356c49db9cb4 100644
--- a/km3io/tools.py
+++ b/km3io/tools.py
@@ -196,7 +196,7 @@ def fitparams():
 
 
 def count_nested(Array, axis=0):
-    """count elements in a nested awkward Array.
+    """Count elements in a nested awkward Array.
 
     Parameters
     ----------