diff --git a/google/genai/_transformers.py b/google/genai/_transformers.py
index 673964713..dd4a85054 100644
--- a/google/genai/_transformers.py
+++ b/google/genai/_transformers.py
@@ -643,15 +643,13 @@ def _raise_for_unsupported_schema_type(origin: Any) -> None:
 def _raise_for_unsupported_mldev_properties(
     schema: Any, client: Optional[_api_client.BaseApiClient]
 ) -> None:
-  if (
-      client
-      and not client.vertexai
-      and (
-          schema.get('additionalProperties')
-          or schema.get('additional_properties')
-      )
+  if client and (
+      schema.get('additionalProperties') or schema.get('additional_properties')
   ):
-    raise ValueError('additionalProperties is only supported in Gemini Enterprise Agent Platform mode, , not in Gemini Developer API mode.')
+    raise ValueError(
+        'additionalProperties is only supported in Gemini Enterprise Agent '
+        'Platform mode, not in Gemini Developer API or Vertex AI mode.'
+    )
 
 
 def process_schema(
diff --git a/google/genai/tests/transformers/test_schema.py b/google/genai/tests/transformers/test_schema.py
index 202bb679b..87ae92379 100644
--- a/google/genai/tests/transformers/test_schema.py
+++ b/google/genai/tests/transformers/test_schema.py
@@ -532,34 +532,11 @@ def test_process_schema_order_properties_propagates_into_additional_properties(
           },
       },
   }
-  schema_without_property_ordering = copy.deepcopy(schema)
-  schema_with_property_ordering = {
-      'type': 'OBJECT',
-      'additionalProperties': {
-          'type': 'OBJECT',
-          'properties': {
-              'foo': {'type': 'STRING'},
-              'bar': {'type': 'STRING'},
-          },
-          'property_ordering': ['foo', 'bar'],
-      },
-  }
-
-  if client.vertexai:
+  with pytest.raises(ValueError) as e:
     _transformers.process_schema(
         schema, client, order_properties=order_properties
     )
-
-    if order_properties:
-      assert schema == schema_with_property_ordering
-    else:
-      assert schema == schema_without_property_ordering
-  else:
-    with pytest.raises(ValueError) as e:
-      _transformers.process_schema(
-          schema, client, order_properties=order_properties
-      )
-    assert 'additionalProperties is only supported in Gemini Enterprise Agent Platform mode' in str(e)
+  assert 'additionalProperties is only supported in Gemini Enterprise Agent Platform mode' in str(e.value)
 
 
 @pytest.mark.parametrize(