diff --git a/homeassistant/components/mqtt/binary_sensor.py b/homeassistant/components/mqtt/binary_sensor.py
index 0ec196270a6..cd69967e6a7 100644
--- a/homeassistant/components/mqtt/binary_sensor.py
+++ b/homeassistant/components/mqtt/binary_sensor.py
@@ -181,7 +181,7 @@ class MqttBinarySensor(
                 expiration_at = dt_util.utcnow() + timedelta(seconds=expire_after)
 
                 self._expiration_trigger = async_track_point_in_utc_time(
-                    self.hass, self.value_is_expired, expiration_at
+                    self.hass, self._value_is_expired, expiration_at
                 )
 
             value_template = self._config.get(CONF_VALUE_TEMPLATE)
@@ -250,7 +250,7 @@ class MqttBinarySensor(
         await MqttDiscoveryUpdate.async_will_remove_from_hass(self)
 
     @callback
-    def value_is_expired(self, *_):
+    def _value_is_expired(self, *_):
         """Triggered when value is expired."""
 
         self._expiration_trigger = None
diff --git a/homeassistant/components/mqtt/sensor.py b/homeassistant/components/mqtt/sensor.py
index 2704c5ae3a1..3ad58468cab 100644
--- a/homeassistant/components/mqtt/sensor.py
+++ b/homeassistant/components/mqtt/sensor.py
@@ -109,6 +109,11 @@ class MqttSensor(
         self._sub_state = None
         self._expiration_trigger = None
 
+        expire_after = config.get(CONF_EXPIRE_AFTER)
+        if expire_after is not None and expire_after > 0:
+            self._expired = True
+        else:
+            self._expired = None
         device_config = config.get(CONF_DEVICE)
 
         MqttAttributes.__init__(self, config)
@@ -145,6 +150,9 @@ class MqttSensor(
             # auto-expire enabled?
             expire_after = self._config.get(CONF_EXPIRE_AFTER)
             if expire_after is not None and expire_after > 0:
+                # When expire_after is set, and we receive a message, assume device is not expired since it has to be to receive the message
+                self._expired = False
+
                 # Reset old trigger
                 if self._expiration_trigger:
                     self._expiration_trigger()
@@ -154,7 +162,7 @@ class MqttSensor(
                 expiration_at = dt_util.utcnow() + timedelta(seconds=expire_after)
 
                 self._expiration_trigger = async_track_point_in_utc_time(
-                    self.hass, self.value_is_expired, expiration_at
+                    self.hass, self._value_is_expired, expiration_at
                 )
 
             if template is not None:
@@ -186,10 +194,10 @@ class MqttSensor(
         await MqttDiscoveryUpdate.async_will_remove_from_hass(self)
 
     @callback
-    def value_is_expired(self, *_):
+    def _value_is_expired(self, *_):
         """Triggered when value is expired."""
         self._expiration_trigger = None
-        self._state = None
+        self._expired = True
         self.async_write_ha_state()
 
     @property
@@ -231,3 +239,12 @@ class MqttSensor(
     def device_class(self) -> Optional[str]:
         """Return the device class of the sensor."""
         return self._config.get(CONF_DEVICE_CLASS)
+
+    @property
+    def available(self) -> bool:
+        """Return true if the device is available and value has not expired."""
+        expire_after = self._config.get(CONF_EXPIRE_AFTER)
+        # pylint: disable=no-member
+        return MqttAvailability.available.fget(self) and (
+            expire_after is None or not self._expired
+        )
diff --git a/tests/components/mqtt/test_sensor.py b/tests/components/mqtt/test_sensor.py
index 19cac2e53c8..5ec5fccbe28 100644
--- a/tests/components/mqtt/test_sensor.py
+++ b/tests/components/mqtt/test_sensor.py
@@ -7,7 +7,7 @@ import pytest
 from homeassistant.components import mqtt
 from homeassistant.components.mqtt.discovery import async_start
 import homeassistant.components.sensor as sensor
-from homeassistant.const import EVENT_STATE_CHANGED
+from homeassistant.const import EVENT_STATE_CHANGED, STATE_UNAVAILABLE
 import homeassistant.core as ha
 from homeassistant.setup import async_setup_component
 import homeassistant.util.dt as dt_util
@@ -73,6 +73,38 @@ async def test_setting_sensor_value_via_mqtt_message(hass, mqtt_mock):
     assert state.attributes.get("unit_of_measurement") == "fav unit"
 
 
+async def test_setting_sensor_value_expires_availability_topic(
+    hass, mqtt_mock, legacy_patchable_time, caplog
+):
+    """Test the expiration of the value."""
+    assert await async_setup_component(
+        hass,
+        sensor.DOMAIN,
+        {
+            sensor.DOMAIN: {
+                "platform": "mqtt",
+                "name": "test",
+                "state_topic": "test-topic",
+                "expire_after": 4,
+                "force_update": True,
+                "availability_topic": "availability-topic",
+            }
+        },
+    )
+    await hass.async_block_till_done()
+
+    state = hass.states.get("sensor.test")
+    assert state.state == STATE_UNAVAILABLE
+
+    async_fire_mqtt_message(hass, "availability-topic", "online")
+
+    # State should be unavailable since expire_after is defined and > 0
+    state = hass.states.get("sensor.test")
+    assert state.state == STATE_UNAVAILABLE
+
+    await expires_helper(hass, mqtt_mock, caplog)
+
+
 async def test_setting_sensor_value_expires(
     hass, mqtt_mock, legacy_patchable_time, caplog
 ):
@@ -93,9 +125,15 @@ async def test_setting_sensor_value_expires(
     )
     await hass.async_block_till_done()
 
+    # State should be unavailable since expire_after is defined and > 0
     state = hass.states.get("sensor.test")
-    assert state.state == "unknown"
+    assert state.state == STATE_UNAVAILABLE
 
+    await expires_helper(hass, mqtt_mock, caplog)
+
+
+async def expires_helper(hass, mqtt_mock, caplog):
+    """Run the basic expiry code."""
     realnow = dt_util.utcnow()
     now = datetime(realnow.year + 1, 1, 1, 1, tzinfo=dt_util.UTC)
     with patch(("homeassistant.helpers.event.dt_util.utcnow"), return_value=now):
@@ -142,7 +180,7 @@ async def test_setting_sensor_value_expires(
 
     # Value is expired now
     state = hass.states.get("sensor.test")
-    assert state.state == "unknown"
+    assert state.state == STATE_UNAVAILABLE
 
 
 async def test_setting_sensor_value_via_mqtt_json_message(hass, mqtt_mock):