diff --git a/tests/lib/streaming/test_messages.py b/tests/lib/streaming/test_messages.py
index e7b649bd..c09baade 100644
--- a/tests/lib/streaming/test_messages.py
+++ b/tests/lib/streaming/test_messages.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import os
+import inspect
 from typing import Any, TypeVar, cast
 from typing_extensions import Iterator, AsyncIterator, override
 
@@ -16,7 +17,7 @@
 base_url = os.environ.get("TEST_API_BASE_URL", "http://127.0.0.1:4010")
 api_key = "my-anthropic-api-key"
 
-client = Anthropic(base_url=base_url, api_key=api_key, _strict_response_validation=True)
+sync_client = Anthropic(base_url=base_url, api_key=api_key, _strict_response_validation=True)
 async_client = AsyncAnthropic(base_url=base_url, api_key=api_key, _strict_response_validation=True)
 
 _T = TypeVar("_T")
@@ -113,7 +114,7 @@ class TestSyncMessages:
     def test_basic_response(self, respx_mock: MockRouter) -> None:
         respx_mock.post("/v1/messages").mock(return_value=httpx.Response(200, content=basic_response()))
 
-        with client.messages.stream(
+        with sync_client.messages.stream(
             max_tokens=1024,
             messages=[
                 {
@@ -133,7 +134,7 @@ def test_basic_response(self, respx_mock: MockRouter) -> None:
     def test_context_manager(self, respx_mock: MockRouter) -> None:
         respx_mock.post("/v1/messages").mock(return_value=httpx.Response(200, content=basic_response()))
 
-        with client.messages.stream(
+        with sync_client.messages.stream(
             max_tokens=1024,
             messages=[
                 {
@@ -190,3 +191,35 @@ async def test_context_manager(self, respx_mock: MockRouter) -> None:
 
         # response should be closed even if the body isn't read
         assert stream.response.is_closed
+
+
+@pytest.mark.parametrize("sync", [True, False], ids=["sync", "async"])
+def test_stream_method_definition_in_sync(sync: bool) -> None:
+    client: Anthropic | AsyncAnthropic = sync_client if sync else async_client
+
+    sig = inspect.signature(client.messages.stream)
+    generated_sig = inspect.signature(client.messages.create)
+
+    errors: list[str] = []
+
+    for name, generated_param in generated_sig.parameters.items():
+        if name == "stream":
+            # intentionally excluded
+            continue
+
+        custom_param = sig.parameters.get(name)
+        if not custom_param:
+            errors.append(f"the `{name}` param is missing")
+            continue
+
+        if custom_param.annotation != generated_param.annotation:
+            errors.append(
+                f"types for the `{name}` param are do not match; generated={repr(generated_param.annotation)} custom={repr(generated_param.annotation)}"
+            )
+            continue
+
+    if errors:
+        raise AssertionError(
+            f"{len(errors)} errors encountered with the {'sync' if sync else 'async'} client `messages.stream()` method:\n\n"
+            + "\n\n".join(errors)
+        )