diff --git a/tests/adapters/test_codex_adapter.py b/tests/adapters/test_codex_adapter.py
index 231bf773f..32cb1bcfe 100644
--- a/tests/adapters/test_codex_adapter.py
+++ b/tests/adapters/test_codex_adapter.py
@@ -888,6 +888,9 @@ def test_codex_logs_into_mcp_server_before_first_turn(
     mock_codex.mcp_auth_statuses["remote"] = adapter.McpAuthStatus.not_logged_in
     open_browser = AsyncMock(return_value=True)
     monkeypatch.setattr(adapter, "_open_authorization_url", open_browser)
+    # Give the login an exact remaining budget, so the rounding check does not
+    # depend on how long the runner takes before the adapter reads the clock.
+    monkeypatch.setattr(adapter, "_remaining_timeout", lambda _: invocation_timeout)
 
     output = invoke_once(codex_payload)