diff --git a/formulaic/transforms/interactions.py b/formulaic/transforms/interactions.py
index b6beeeb..a9b4824 100644
--- a/formulaic/transforms/interactions.py
+++ b/formulaic/transforms/interactions.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from typing import TYPE_CHECKING, Any
 
 import narwhals.stable.v1 as narwhals