diff --git a/homeassistant/components/sensor/systemmonitor.py b/homeassistant/components/sensor/systemmonitor.py
index 99e2453c4871fd0689bfd449fdeedabe9f6fb8c8..e03e987802bef32e9ed0210d03d2d50531326ed0 100644
--- a/homeassistant/components/sensor/systemmonitor.py
+++ b/homeassistant/components/sensor/systemmonitor.py
@@ -50,7 +50,7 @@ class SystemMonitorSensor(Entity):
         self.argument = argument
         self.type = sensor_type
         self._state = None
-        self.unit_of_measurement = SENSOR_TYPES[sensor_type][1]
+        self._unit_of_measurement = SENSOR_TYPES[sensor_type][1]
         self.update()
 
     @property
@@ -62,6 +62,10 @@ class SystemMonitorSensor(Entity):
         """ Returns the state of the device. """
         return self._state
 
+    @property
+    def unit_of_measurement(self):
+        return self._unit_of_measurement
+
     def update(self):
         if self.type == 'disk_use_percent':
             self._state = psutil.disk_usage(self.argument).percent
diff --git a/homeassistant/components/sensor/tellstick.py b/homeassistant/components/sensor/tellstick.py
index 699821fa6b6c32576a8783c56f7f204b60902fe7..5720b65a669b28a730c13cec5ff0d7f8418e208d 100644
--- a/homeassistant/components/sensor/tellstick.py
+++ b/homeassistant/components/sensor/tellstick.py
@@ -99,7 +99,7 @@ class TellstickSensor(Entity):
     def __init__(self, name, sensor, datatype, sensor_info):
         self.datatype = datatype
         self.sensor = sensor
-        self.unit_of_measurement = sensor_info.unit or None
+        self._unit_of_measurement = sensor_info.unit or None
 
         self._name = "{} {}".format(name, sensor_info.name)
 
@@ -112,3 +112,7 @@ class TellstickSensor(Entity):
     def state(self):
         """ Returns the state of the device. """
         return self.sensor.value(self.datatype).value
+
+    @property
+    def unit_of_measurement(self):
+        return self._unit_of_measurement