diff --git a/test/web_interface/test_api_v3_backup_restore.py b/test/web_interface/test_api_v3_backup_restore.py
index 52758fba..4c4a8304 100644
--- a/test/web_interface/test_api_v3_backup_restore.py
+++ b/test/web_interface/test_api_v3_backup_restore.py
@@ -139,6 +139,23 @@ class TestRequestValidation:
         assert post(client, options="{}").status_code == 200
         assert restore.call_args[0][2].restore_config is True
 
+    def test_unknown_option_key_is_refused(self, client, restore):
+        # Regression: opts_dict.get('restore_secrets', True) silently
+        # ignores a typo'd/renamed key like "restoreSecrets" and keeps the
+        # True default, restoring secrets a caller's request clearly meant
+        # to exclude -- with no indication anything was wrong.
+        response = post(client, options=json.dumps({"restoreSecrets": False}))
+        assert response.status_code == 400
+        assert "Unknown restore option" in response.get_json()["message"]
+        assert "restoreSecrets" in response.get_json()["message"]
+        restore.assert_not_called()
+
+    def test_known_and_unknown_keys_together_are_refused(self, client, restore):
+        response = post(client, options=json.dumps({
+            "restore_secrets": False, "restore_everything": True}))
+        assert response.status_code == 400
+        restore.assert_not_called()
+
 
 class TestOptionsAreBooleanAware:
     """Regression: bool("false") is True in Python.
diff --git a/web_interface/blueprints/api_v3/backup.py b/web_interface/blueprints/api_v3/backup.py
index f971f0e7..53e3a12d 100644
--- a/web_interface/blueprints/api_v3/backup.py
+++ b/web_interface/blueprints/api_v3/backup.py
@@ -90,6 +90,14 @@ def backup_validate():
     except Exception as e:
         logger.error("backup_validate failed: %s", e, exc_info=True)
         return jsonify({'status': 'error', 'message': 'An internal error occurred; see logs for details'}), 500
+#: The only keys RestoreOptions recognizes. A typo'd or renamed key (e.g.
+#: "restoreSecrets") would otherwise be silently ignored by opts_dict.get(),
+#: leaving that flag at its True default -- restoring secrets a caller's
+#: request clearly meant to exclude, with no indication anything was wrong.
+_RESTORE_OPTION_KEYS = frozenset((
+    'restore_config', 'restore_secrets', 'restore_wifi', 'restore_fonts',
+    'restore_plugin_uploads', 'reinstall_plugins',
+))
 @api_v3.route('/backup/restore', methods=['POST'])
 def backup_restore():
     """Restore a backup ZIP with optional RestoreOptions."""
@@ -112,6 +120,12 @@ def backup_restore():
                 'status': 'error',
                 'message': 'Invalid options: expected a JSON object',
             }), 400
+        unknown_keys = set(opts_dict) - _RESTORE_OPTION_KEYS
+        if unknown_keys:
+            return jsonify({
+                'status': 'error',
+                'message': f'Unknown restore option(s): {", ".join(sorted(unknown_keys))}',
+            }), 400
         # _coerce_to_bool (not bare bool()) because a request can send these
         # as JSON strings: bool("false") is True in Python, so a caller who
         # explicitly asked to skip secrets would have had them restored