diff --git a/pyproject.toml b/pyproject.toml
index 9d30c3d626a..e17f44c6b43 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -2,7 +2,7 @@
 requires = [
     "setuptools>=41.0.0,<50.0",
     "wheel",
-    "cython",
+    "cython<3.0",
     "oldest-supported-numpy",
     "sphinx",
     "recommonmark",