diff --git a/pyproject.toml b/pyproject.toml
index 175038c..86f6aca 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -3,6 +3,7 @@ requires = ["setuptools >= 63.0.0", "wheel", "setuptools-scm"]
 build-backend = "setuptools.build_meta"
 
 [project]
+requires-python = ">=3.9"
 name = "corrlib"
 dynamic = ["version"]
 dependencies = [