diff --git a/h3ronpy/pyproject.toml b/h3ronpy/pyproject.toml
index 95aa294..e280c37 100644
--- a/h3ronpy/pyproject.toml
+++ b/h3ronpy/pyproject.toml
@@ -33,6 +33,7 @@ classifiers = [
     "Topic :: Scientific/Engineering :: GIS",
     "License :: OSI Approved :: MIT License",
 ]
+requires-python = ">=3.9"
 
 
 [project.optional-dependencies]