diff --git a/pytec/tec_qt.py b/pytec/tec_qt.py
index db81e1c..2e60e1d 100644
--- a/pytec/tec_qt.py
+++ b/pytec/tec_qt.py
@@ -279,9 +279,9 @@ class MainWindow(QtWidgets.QMainWindow):
                         set_param_args = (*thermostat_param[:2], "off")
                     else:
                         set_param_args = (*thermostat_param, new_value)
-                    param.child(*param.childPath(inner_param)).setOpts(lock=True)
+                    inner_param.setOpts(lock=True)
                     await self.client.set_param(*set_param_args)
-                    param.child(*param.childPath(inner_param)).setOpts(lock=False)
+                    inner_param.setOpts(lock=False)
 
                 if "pid_autotune" in inner_param.opts:
                     auto_tuner_param = inner_param.opts["pid_autotune"][0]