diff --git a/tests/unit/proxy/test_sse_error_frame_convention.py b/tests/unit/proxy/test_sse_error_frame_convention.py
index f84d863daf7..a4909e40be0 100644
--- a/tests/unit/proxy/test_sse_error_frame_convention.py
+++ b/tests/unit/proxy/test_sse_error_frame_convention.py
@@ -7,6 +7,8 @@ event and is skipped, so a failure delivered that way never reaches the caller.
 from __future__ import annotations
 
 import json
+from typing import cast
+from unittest.mock import MagicMock
 
 import pytest
 from starlette.requests import Request
@@ -33,6 +35,16 @@ def test_openai_paths_are_left_alone() -> None:
     assert not _streams_anthropic_events(None)
 
 
+def test_a_request_without_a_real_path_is_not_anthropic() -> None:
+    """A mocked or partial request must not be read as an Anthropic caller."""
+
+    class _MockedRequest:
+        url = MagicMock()
+
+    assert not _streams_anthropic_events(cast(Request, _MockedRequest()))
+    assert not _streams_anthropic_events(cast(Request, MagicMock()))
+
+
 def test_anthropic_frame_is_an_error_event_without_done() -> None:
     frames = _anthropic_sse_error_frames({"message": "boom", "type": "internal_server_error", "code": "500"})