diff --git a/pymf/tb/tb.py b/pymf/tb/tb.py
index ed0a50367c2b7cda7782628f0dcc6a59b9433341..52678b846096341fdf33d7bae9b0f645a050c27d 100644
--- a/pymf/tb/tb.py
+++ b/pymf/tb/tb.py
@@ -1,6 +1,6 @@
 import numpy as np
 
-tb_type = dict[tuple[None] | tuple[int, ...], np.ndarray]
+tb_type = dict[tuple[()] | tuple[int, ...], np.ndarray]
 
 
 def add_tb(tb1: tb_type, tb2: tb_type) -> tb_type: