diff --git a/tests/test_arbitrary_types.py b/tests/test_arbitrary_types.py
new file mode 100644
index 000000000..8b8417bae
--- /dev/null
+++ b/tests/test_arbitrary_types.py
@@ -0,0 +1,140 @@
+from typing import Annotated
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from inline_snapshot import snapshot
+
+from .utils import needs_pydanticv2
+
+
+@pytest.fixture(name="client")
+def get_client():
+    from pydantic import (
+        BaseModel,
+        ConfigDict,
+        PlainSerializer,
+        TypeAdapter,
+        WithJsonSchema,
+    )
+
+    class FakeNumpyArray:
+        def __init__(self):
+            self.data = [1.0, 2.0, 3.0]
+
+    FakeNumpyArrayPydantic = Annotated[
+        FakeNumpyArray,
+        WithJsonSchema(TypeAdapter(list[float]).json_schema()),
+        PlainSerializer(lambda v: v.data),
+    ]
+
+    class MyModel(BaseModel):
+        model_config = ConfigDict(arbitrary_types_allowed=True)
+        custom_field: FakeNumpyArrayPydantic
+
+    app = FastAPI()
+
+    @app.get("/")
+    def test() -> MyModel:
+        return MyModel(custom_field=FakeNumpyArray())
+
+    client = TestClient(app)
+    return client
+
+
+@needs_pydanticv2
+def test_get(client: TestClient):
+    response = client.get("/")
+    assert response.json() == {"custom_field": [1.0, 2.0, 3.0]}
+
+
+@needs_pydanticv2
+def test_typeadapter():
+    # This test is only to confirm that Pydantic alone is working as expected
+    from pydantic import (
+        BaseModel,
+        ConfigDict,
+        PlainSerializer,
+        TypeAdapter,
+        WithJsonSchema,
+    )
+
+    class FakeNumpyArray:
+        def __init__(self):
+            self.data = [1.0, 2.0, 3.0]
+
+    FakeNumpyArrayPydantic = Annotated[
+        FakeNumpyArray,
+        WithJsonSchema(TypeAdapter(list[float]).json_schema()),
+        PlainSerializer(lambda v: v.data),
+    ]
+
+    class MyModel(BaseModel):
+        model_config = ConfigDict(arbitrary_types_allowed=True)
+        custom_field: FakeNumpyArrayPydantic
+
+    ta = TypeAdapter(MyModel)
+    assert ta.dump_python(MyModel(custom_field=FakeNumpyArray())) == {
+        "custom_field": [1.0, 2.0, 3.0]
+    }
+    assert ta.json_schema() == snapshot(
+        {
+            "properties": {
+                "custom_field": {
+                    "items": {"type": "number"},
+                    "title": "Custom Field",
+                    "type": "array",
+                }
+            },
+            "required": ["custom_field"],
+            "title": "MyModel",
+            "type": "object",
+        }
+    )
+
+
+@needs_pydanticv2
+def test_openapi_schema(client: TestClient):
+    response = client.get("openapi.json")
+    assert response.json() == snapshot(
+        {
+            "openapi": "3.1.0",
+            "info": {"title": "FastAPI", "version": "0.1.0"},
+            "paths": {
+                "/": {
+                    "get": {
+                        "summary": "Test",
+                        "operationId": "test__get",
+                        "responses": {
+                            "200": {
+                                "description": "Successful Response",
+                                "content": {
+                                    "application/json": {
+                                        "schema": {
+                                            "$ref": "#/components/schemas/MyModel"
+                                        }
+                                    }
+                                },
+                            }
+                        },
+                    }
+                }
+            },
+            "components": {
+                "schemas": {
+                    "MyModel": {
+                        "properties": {
+                            "custom_field": {
+                                "items": {"type": "number"},
+                                "type": "array",
+                                "title": "Custom Field",
+                            }
+                        },
+                        "type": "object",
+                        "required": ["custom_field"],
+                        "title": "MyModel",
+                    }
+                }
+            },
+        }
+    )