diff --git a/ohmpi/hardware_system.py b/ohmpi/hardware_system.py
index cc0e31a039768a14e8470c287ddf6828b4ea8330..bdf03b00c91571b40f740c416414026b7a6eb0e6 100644
--- a/ohmpi/hardware_system.py
+++ b/ohmpi/hardware_system.py
@@ -108,9 +108,9 @@ class OhmPiHardware:
             mux_module = importlib.import_module(f'ohmpi.hardware_components.{mux_config["model"]}')
             if isinstance(mux_config['ctl'], dict): ### TODO: is this needed?
                 mux_ctl_module = importlib.import_module(f'ohmpi.hardware_components.{mux_config["ctl"]["model"]}')
-                ctl = mux_ctl_module.Ctl(**mux_config['ctl'])  # (**self.ctl)
+                mux_config['ctl'] = mux_ctl_module.Ctl(**mux_config['ctl'])  # (**self.ctl)
             assert issubclass(type(mux_config['ctl']), CtlAbstract)
-            io = mux_config.pop('io', ctl.connections[mux_config.pop('connection', 'i2c')])
+            io = mux_config.pop('io', mux_config['ctl'].connections[mux_config.pop('connection', 'i2c')])
             mux_config.update({'io': io})
             mux_config['id'] = mux_id