diff --git a/src/bentoml/_internal/service/openapi/specification.py b/src/bentoml/_internal/service/openapi/specification.py
index 843d298e221..f3e86b274bf 100644
--- a/src/bentoml/_internal/service/openapi/specification.py
+++ b/src/bentoml/_internal/service/openapi/specification.py
@@ -104,7 +104,7 @@ class Schema:
     anyOf: t.Optional[t.List[Schema]] = None
     not_: t.Optional[Schema] = None
     items: t.Optional[t.Union[Schema, t.List[Schema]]] = None
-    properties: t.Optional[t.Dict[str, Schema | Reference]] = None
+    properties: t.Optional[t.Dict[str, t.Union[Schema, Reference]]] = None
     additionalProperties: t.Optional[t.Union[Schema, Reference, bool]] = None
     description: t.Optional[str] = None
     format: t.Optional[str] = None
diff --git a/tests/unit/_internal/io/test_numpy.py b/tests/unit/_internal/io/test_numpy.py
index 5aab59e484c..2c9b4477c3f 100644
--- a/tests/unit/_internal/io/test_numpy.py
+++ b/tests/unit/_internal/io/test_numpy.py
@@ -85,6 +85,8 @@ def test_numpy_openapi_request_body():
 
     nparray = NumpyNdarray(dtype="float")
     nparray.sample_input = ExampleGeneric("asdf")  # type: ignore (test exception)
+    with pytest.raises(BadInput):
+        nparray.openapi_example()
 
 
 def test_numpy_openapi_responses():