diff --git a/snarl/types.py b/snarl/types.py
index 54482c4..ec2b4c6 100644
--- a/snarl/types.py
+++ b/snarl/types.py
@@ -1,5 +1,5 @@
-from typing import Union, Tuple, List, Sequence, Optional
+from typing import Union, Tuple, List, Sequence, Optional, Hashable
 
-layer_t = Tuple[int, int]
+layer_t = Hashable
 contour_t = List[Tuple[int, int]]
 connectivity_t = Sequence[Tuple[layer_t, Optional[layer_t], layer_t]]