diff --git a/pyproject.toml b/pyproject.toml
index e2a2a64a3..c535b7f6a 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,7 +30,7 @@ dependencies = [
   "jsonschema>=4.23",
   "ml-dtypes>=0.5.3",
   "numpy>=2.2,<2.3",
-  "onnx==1.18",
+  "onnx==1.21.0",
   "onnx-ir>=0.1",
   "onnxruntime-windowsml>=1.23.2,<1.24.0",
   "onnxscript>=0.2",