diff --git a/pyproject.toml b/pyproject.toml
index 8946355d..26e9d4ad 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -28,6 +28,7 @@ readme = "README.rst"
 dependencies = [
     "scikit-learn>=1.1, !=1.5.0",
     "derivative>=0.6.2",
+    "typing_extensions",
 ]
 
 [project.optional-dependencies]