diff --git a/tests/tools/test_exec_platform.py b/tests/tools/test_exec_platform.py
index 890c8b29b..637a3ec60 100644
--- a/tests/tools/test_exec_platform.py
+++ b/tests/tools/test_exec_platform.py
@@ -160,7 +160,7 @@ class TestSpawnWindows:
 
         with (
             patch("nanobot.agent.tools.shell._IS_WINDOWS", True),
-            patch("nanobot.agent.tools.shell.sys.platform", "win32"),
+            patch("nanobot.agent.tools.shell.sys", MagicMock(platform="win32")),
             patch("asyncio.create_subprocess_exec", new_callable=AsyncMock) as mock_exec,
             patch.object(ExecTool, "_create_windows_job", return_value=job),
             pytest.raises(OSError, match="OpenProcess failed"),