diff --git a/src/skan/csr.py b/src/skan/csr.py
index 279e55f8..72b6a39b 100644
--- a/src/skan/csr.py
+++ b/src/skan/csr.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import numpy as np
 import pandas as pd
 from scipy import sparse, ndimage as ndi