diff --git a/pyproject.toml b/pyproject.toml
index 6fe5eb6..46256d8 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -19,6 +19,7 @@ scikit-fmm = "^2022.03.26"
 simpleitk = "2.0.2"
 matplotlib = "3.4.2"
 torch = "1.10.0"
+naturalneighbor = "^0.2.1"
 
 
 [tool.poetry.dev-dependencies]