diff --git a/tests/integration/mcp/test_mcp_agent_365_guardrail.py b/tests/integration/mcp/test_mcp_agent_365_guardrail.py
index 6f8aea462f8..f3c923cbf10 100644
--- a/tests/integration/mcp/test_mcp_agent_365_guardrail.py
+++ b/tests/integration/mcp/test_mcp_agent_365_guardrail.py
@@ -38,6 +38,10 @@ GUARDRAIL_ROWS: Final = (
 FALLBACKS: Final = (None, "fail_open", "fail_closed")
 
 
+def _origin(gateway: Gateway) -> str:
+    return str(gateway.client.base_url).rstrip("/")
+
+
 def _generic_guardrail_outage(request: Request) -> Reply:
     assert request.target == "/beta/litellm_basic_guardrail_api", request.target
     return Reply(status=503, body=json.dumps({"error": "synthetic sibling guardrail outage"}).encode())
@@ -136,17 +140,21 @@ def test_a_missing_or_malformed_caller_bearer_blocks_on_every_entry_point_whatev
 ) -> None:
     with _rig(gateway, tmp_path, fallback) as rig:
         assert f"{rig.alias}-add" in rig.caller().list_tools().tools, "the catalog needs only the virtual key"
+        metadata_url: Final = f"{_origin(rig.candidate)}/.well-known/oauth-protected-resource/{rig.alias}/mcp"
         for entry in ENTRY_POINTS:
-            missing: Final = rig.caller(entry).call(f"{rig.alias}-add", {"entry": entry}, server_id=rig.server_id)
-            malformed: Final = rig.caller(entry, "not-a-jws").call(
-                f"{rig.alias}-add", {"entry": entry}, server_id=rig.server_id
-            )
-            for label, outcome in (("without a bearer", missing), ("opaque bearer", malformed)):
-                assert outcome.error is not None, f"{entry} {label}: {outcome.raw}"
+            for label, bearer in (("without a bearer", None), ("opaque bearer", "not-a-jws")):
+                caller: Final = rig.caller(entry, bearer)
                 if entry == "server_mcp":
-                    assert outcome.status == 401, f"{entry} {label} skips the connect sign-in challenge: {outcome.raw}"
-                else:
-                    assert REJECTED in outcome.raw, f"{entry} {label}: {outcome.raw}"
+                    challenged: Final = caller.rpc(
+                        "tools/call", {"name": f"{rig.alias}-add", "arguments": {"entry": entry}}
+                    )
+                    assert challenged.status_code == 401, f"{entry} {label}: {challenged.text}"
+                    authenticate: Final = challenged.headers.get("www-authenticate", "")
+                    assert f'resource_metadata="{metadata_url}"' in authenticate, f"{entry} {label}: {authenticate!r}"
+                    assert 'error="invalid_token"' in authenticate, f"{entry} {label}: {authenticate!r}"
+                    continue
+                outcome: Final = caller.call(f"{rig.alias}-add", {"entry": entry}, server_id=rig.server_id)
+                assert outcome.error is not None and REJECTED in outcome.raw, f"{entry} {label}: {outcome.raw}"
         assert rig.upstream_tool_names() == ()
         expected: Final = 2 * (len(ENTRY_POINTS) - 1)
         assert rig.guardrail_statuses("call_mcp_tool", expected) == ["guardrail_intervened"] * expected