diff --git a/pymf/tb/tb.py b/pymf/tb/tb.py
index 445a99b483292f885368842b52a240c9e86f1ab3..3f193cf73db4cfb08302a035e68430cf3ec44f8f 100644
--- a/pymf/tb/tb.py
+++ b/pymf/tb/tb.py
@@ -1,6 +1,6 @@
 import numpy as np
 
-_tb_type = dict[tuple[()] | tuple[int, ...], np.ndarray]
+_tb_type = dict[tuple[int, ...], np.ndarray]
 
 
 def add_tb(tb1: _tb_type, tb2: _tb_type) -> _tb_type: