diff --git a/lenskit/pyproject.toml b/lenskit/pyproject.toml
index 3be35a4d4..bfa38dd43 100644
--- a/lenskit/pyproject.toml
+++ b/lenskit/pyproject.toml
@@ -21,7 +21,7 @@ license = { file = "LICENSE.md" }
 dynamic = ["version"]
 dependencies = [
   "pandas >=1.5, <3",
-  "numpy >= 1.23",
+  "numpy >= 1.23,<2",
   "scipy >= 1.9.0",
   "torch ~=2.1",            # conda: pytorch>=2.1,<3
   "threadpoolctl >=3.0",