diff --git a/hermes_cli/main.py b/hermes_cli/main.py
index c56fc1e3..70a30ab5 100644
--- a/hermes_cli/main.py
+++ b/hermes_cli/main.py
@@ -5274,12 +5274,13 @@ def _warn_stale_dashboard_processes() -> None:
 
     try:
         if sys.platform == "win32":
-            # wmic emits text in the system code page (e.g. cp936 on zh-CN
-            # locales), not UTF-8. Without an explicit encoding, Python's
-            # default UTF-8 decoder crashes the subprocess reader thread
-            # with UnicodeDecodeError, leaving result.stdout=None and the
-            # subsequent .split() call crashing `hermes update` with an
-            # AttributeError on Windows non-UTF-8 locales (#17049).
+            # wmic may emit text in the system code page (for example cp936
+            # on zh-CN systems), not UTF-8. In text mode, subprocess output
+            # decoding depends on Python's configuration (locale-dependent
+            # by default, or UTF-8 in UTF-8 mode). The important protection
+            # here is errors="ignore": it prevents a reader-thread
+            # UnicodeDecodeError from leaving result.stdout=None and turning
+            # the later .split() into an AttributeError (#17049).
             result = subprocess.run(
                 ["wmic", "process", "get", "ProcessId,CommandLine",
                  "/FORMAT:LIST"],
diff --git a/tests/hermes_cli/test_update_stale_dashboard.py b/tests/hermes_cli/test_update_stale_dashboard.py
index b36f9e5a..20f23e58 100644
--- a/tests/hermes_cli/test_update_stale_dashboard.py
+++ b/tests/hermes_cli/test_update_stale_dashboard.py
@@ -182,13 +182,12 @@ class TestWindowsWmicEncoding:
     `hermes update` on non-UTF-8 system locales (e.g. cp936 on zh-CN).
     """
 
-    def test_wmic_invoked_with_utf8_ignore_errors(self):
+    def test_wmic_invoked_with_utf8_ignore_errors(self, monkeypatch):
         """The wmic subprocess.run call must pass encoding='utf-8' and
         errors='ignore' so the subprocess reader thread cannot raise
         UnicodeDecodeError on non-UTF-8 wmic output."""
-        with patch("hermes_cli.main.sys") as mock_sys, \
-                patch("subprocess.run") as mock_run:
-            mock_sys.platform = "win32"
+        monkeypatch.setattr(sys, "platform", "win32")
+        with patch("subprocess.run") as mock_run:
             # Provide a minimal valid wmic /FORMAT:LIST response.
             mock_run.return_value = MagicMock(
                 returncode=0,
@@ -212,15 +211,14 @@ class TestWindowsWmicEncoding:
             "down the reader thread (#17049)."
         )
 
-    def test_wmic_returns_none_stdout_does_not_crash(self, capsys):
+    def test_wmic_returns_none_stdout_does_not_crash(self, monkeypatch, capsys):
         """If subprocess.run returns successfully but stdout is None — which
         is what Python 3.11 leaves behind when the reader thread silently
         crashed on UnicodeDecodeError before this fix landed — the warning
         must short-circuit instead of raising AttributeError on
         ``None.split('\\n')`` and aborting `hermes update` (#17049)."""
-        with patch("hermes_cli.main.sys") as mock_sys, \
-                patch("subprocess.run") as mock_run:
-            mock_sys.platform = "win32"
+        monkeypatch.setattr(sys, "platform", "win32")
+        with patch("subprocess.run") as mock_run:
             mock_run.return_value = MagicMock(
                 returncode=0, stdout=None, stderr=""
             )