diff --git a/pyproject.toml b/pyproject.toml
index f885fae..6b91294 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,7 +30,8 @@ classifiers = [
 ]
 requires-python = ">=3.9"
 dependencies = [
-    "numpy",
+    "numpy<2.0 ; python_version <= '3.9'",
+    "numpy ; python_version >= '3.10'",
     "pint",
     "pyg4ometry",
     "pylegendmeta>=v0.9.0a2",