diff --git a/homeassistant/components/demo/sensor.py b/homeassistant/components/demo/sensor.py
index 7607bad4e1c..00111d34dd4 100644
--- a/homeassistant/components/demo/sensor.py
+++ b/homeassistant/components/demo/sensor.py
@@ -1,5 +1,5 @@
 """Demo platform that has a couple of fake sensors."""
-from homeassistant.components.sensor import SensorEntity
+from homeassistant.components.sensor import STATE_CLASS_MEASUREMENT, SensorEntity
 from homeassistant.const import (
     ATTR_BATTERY_LEVEL,
     CONCENTRATION_PARTS_PER_MILLION,
@@ -23,6 +23,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
                 "Outside Temperature",
                 15.6,
                 DEVICE_CLASS_TEMPERATURE,
+                STATE_CLASS_MEASUREMENT,
                 TEMP_CELSIUS,
                 12,
             ),
@@ -31,6 +32,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
                 "Outside Humidity",
                 54,
                 DEVICE_CLASS_HUMIDITY,
+                STATE_CLASS_MEASUREMENT,
                 PERCENTAGE,
                 None,
             ),
@@ -39,6 +41,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
                 "Carbon monoxide",
                 54,
                 DEVICE_CLASS_CO,
+                STATE_CLASS_MEASUREMENT,
                 CONCENTRATION_PARTS_PER_MILLION,
                 None,
             ),
@@ -47,6 +50,7 @@ async def async_setup_platform(hass, config, async_add_entities, discovery_info=
                 "Carbon dioxide",
                 54,
                 DEVICE_CLASS_CO2,
+                STATE_CLASS_MEASUREMENT,
                 CONCENTRATION_PARTS_PER_MILLION,
                 14,
             ),
@@ -63,15 +67,23 @@ class DemoSensor(SensorEntity):
     """Representation of a Demo sensor."""
 
     def __init__(
-        self, unique_id, name, state, device_class, unit_of_measurement, battery
+        self,
+        unique_id,
+        name,
+        state,
+        device_class,
+        state_class,
+        unit_of_measurement,
+        battery,
     ):
         """Initialize the sensor."""
-        self._unique_id = unique_id
+        self._battery = battery
+        self._device_class = device_class
         self._name = name
         self._state = state
-        self._device_class = device_class
+        self._state_class = state_class
+        self._unique_id = unique_id
         self._unit_of_measurement = unit_of_measurement
-        self._battery = battery
 
     @property
     def device_info(self):
@@ -99,6 +111,11 @@ class DemoSensor(SensorEntity):
         """Return the device class of the sensor."""
         return self._device_class
 
+    @property
+    def state_class(self):
+        """Return the state class of the sensor."""
+        return self._state_class
+
     @property
     def name(self):
         """Return the name of the sensor."""
diff --git a/tests/components/prometheus/test_init.py b/tests/components/prometheus/test_init.py
index fe91c7c0002..b1abe1de3e5 100644
--- a/tests/components/prometheus/test_init.py
+++ b/tests/components/prometheus/test_init.py
@@ -47,14 +47,14 @@ async def prometheus_client(hass, hass_client):
     )
 
     sensor1 = DemoSensor(
-        None, "Television Energy", 74, None, ENERGY_KILO_WATT_HOUR, None
+        None, "Television Energy", 74, None, None, ENERGY_KILO_WATT_HOUR, None
     )
     sensor1.hass = hass
     sensor1.entity_id = "sensor.television_energy"
     await sensor1.async_update_ha_state()
 
     sensor2 = DemoSensor(
-        None, "Radio Energy", 14, DEVICE_CLASS_POWER, ENERGY_KILO_WATT_HOUR, None
+        None, "Radio Energy", 14, DEVICE_CLASS_POWER, None, ENERGY_KILO_WATT_HOUR, None
     )
     sensor2.hass = hass
     sensor2.entity_id = "sensor.radio_energy"
@@ -65,13 +65,19 @@ async def prometheus_client(hass, hass_client):
         await sensor2.async_update_ha_state()
 
     sensor3 = DemoSensor(
-        None, "Electricity price", 0.123, None, f"SEK/{ENERGY_KILO_WATT_HOUR}", None
+        None,
+        "Electricity price",
+        0.123,
+        None,
+        None,
+        f"SEK/{ENERGY_KILO_WATT_HOUR}",
+        None,
     )
     sensor3.hass = hass
     sensor3.entity_id = "sensor.electricity_price"
     await sensor3.async_update_ha_state()
 
-    sensor4 = DemoSensor(None, "Wind Direction", 25, None, DEGREE, None)
+    sensor4 = DemoSensor(None, "Wind Direction", 25, None, None, DEGREE, None)
     sensor4.hass = hass
     sensor4.entity_id = "sensor.wind_direction"
     await sensor4.async_update_ha_state()
@@ -81,6 +87,7 @@ async def prometheus_client(hass, hass_client):
         "SPS30 PM <1µm Weight concentration",
         3.7069,
         None,
+        None,
         CONCENTRATION_MICROGRAMS_PER_CUBIC_METER,
         None,
     )