diff --git a/src/tests/test_logger.py b/src/tests/test_logger.py
index 5bc67dd..c020055 100644
--- a/src/tests/test_logger.py
+++ b/src/tests/test_logger.py
@@ -1,6 +1,9 @@
 from unittest.mock import patch
+import pytest
+from fastapi import Request
 from fastapi.testclient import TestClient
 from app.main import app
+from app.middleware.logging import RequestLoggingMiddleware, request_id_var
 
 client = TestClient(app)
 
@@ -32,6 +35,39 @@ def test_x_request_id_passed():
         mock_logger.assert_called_once()
 
 
+@pytest.mark.anyio
+async def test_logger_middleware_unit_exception():
+    # Unit test RequestLoggingMiddleware directly when call_next raises an exception.
+    middleware = RequestLoggingMiddleware(app)
+    mock_request = Request(
+        {
+            "type": "http",
+            "method": "GET",
+            "path": "/error-test",
+            "headers": [(b"x-request-id", b"unit-test-id")],
+        }
+    )
+
+    async def mock_call_next(req):
+        raise RuntimeError("Downstream failure")
+
+    with patch("app.middleware.logging.logger.info") as mock_logger:
+        with pytest.raises(RuntimeError, match="Downstream failure"):
+            await middleware.dispatch(mock_request, mock_call_next)
+
+        mock_logger.assert_called_once()
+        args, kwargs = mock_logger.call_args
+
+        assert "GET /error-test - 500" in args[0]
+        assert kwargs["extra"]["path"] == "/error-test"
+        assert kwargs["extra"]["method"] == "GET"
+        assert kwargs["extra"]["status_code"] == 500
+        assert "latency" in kwargs["extra"]
+
+    # Verify contextvar request_id_var was properly reset
+    assert request_id_var.get() == ""
+
+
 def test_json_formatter_redacts_exception_pii():
     import json
     import logging
diff --git a/src/tests/test_security_headers.py b/src/tests/test_security_headers.py
index b9afd55..7e3ef65 100644
--- a/src/tests/test_security_headers.py
+++ b/src/tests/test_security_headers.py
@@ -1,3 +1,4 @@
+from unittest.mock import patch
 from fastapi.testclient import TestClient
 from app.main import app
 
@@ -32,3 +33,28 @@ def test_security_headers():
         headers["Content-Security-Policy"]
         == "default-src 'self'; frame-ancestors 'none';"
     )
+
+
+def test_security_headers_on_500_exception():
+    # Test that security headers are present on 500 Internal Server Error responses
+    err_client = TestClient(app, raise_server_exceptions=False)
+    with patch("app.main.get_model", side_effect=RuntimeError("Unexpected error")):
+        response = err_client.post(
+            "/v1/embeddings", json={"input": "test", "model": "cl-nagoya/ruri-v3-30m"}
+        )
+
+    assert response.status_code == 500
+    headers = response.headers
+
+    assert headers.get("X-Content-Type-Options") == "nosniff"
+    assert headers.get("X-Frame-Options") == "DENY"
+    assert headers.get("X-XSS-Protection") == "1; mode=block"
+    assert (
+        headers.get("Strict-Transport-Security")
+        == "max-age=31536000; includeSubDomains"
+    )
+    assert headers.get("Referrer-Policy") == "strict-origin-when-cross-origin"
+    assert (
+        headers.get("Content-Security-Policy")
+        == "default-src 'self'; frame-ancestors 'none';"
+    )