diff --git a/tests/test_config_manager.py b/tests/test_config_manager.py
index dad2f10..142c9c3 100644
--- a/tests/test_config_manager.py
+++ b/tests/test_config_manager.py
@@ -604,13 +604,23 @@ class TestTypedAccessors(unittest.TestCase):
         self.assertEqual(advanced["whispercpp_n_threads"], 0)
 
     def test_whispercpp_advanced_persistence(self):
-        self.config_manager.set("advanced", "whispercpp_temperature", 0.5)
-        self.config_manager.set("advanced", "whispercpp_no_timestamps", False)
-        self.config_manager.set("advanced", "whispercpp_initial_prompt", "Meeting notes")
-        self.config_manager.save_config()
+        # This class skips ConfigManager.__init__, so unlike TestConfigManager
+        # nothing has redirected CONFIG_FILE: without the patches below this
+        # save_config() overwrites the developer's real ~/.config/vocalinux/
+        # config.json with the synthetic fixture from setUp.
+        with tempfile.TemporaryDirectory() as temp_dir:
+            temp_file = os.path.join(temp_dir, "config.json")
+            with (
+                patch("vocalinux.ui.config_manager.CONFIG_DIR", temp_dir),
+                patch("vocalinux.ui.config_manager.CONFIG_FILE", temp_file),
+            ):
+                self.config_manager.set("advanced", "whispercpp_temperature", 0.5)
+                self.config_manager.set("advanced", "whispercpp_no_timestamps", False)
+                self.config_manager.set("advanced", "whispercpp_initial_prompt", "Meeting notes")
+                self.config_manager.save_config()
 
-        new_manager = ConfigManager()
-        advanced = new_manager.get_settings().get("advanced", {})
-        self.assertEqual(advanced["whispercpp_temperature"], 0.5)
-        self.assertFalse(advanced["whispercpp_no_timestamps"])
-        self.assertEqual(advanced["whispercpp_initial_prompt"], "Meeting notes")
+                new_manager = ConfigManager()
+                advanced = new_manager.get_settings().get("advanced", {})
+                self.assertEqual(advanced["whispercpp_temperature"], 0.5)
+                self.assertFalse(advanced["whispercpp_no_timestamps"])
+                self.assertEqual(advanced["whispercpp_initial_prompt"], "Meeting notes")