diff --git a/homeassistant/components/threshold/binary_sensor.py b/homeassistant/components/threshold/binary_sensor.py
index 5bd6f77253b..1a53a599394 100644
--- a/homeassistant/components/threshold/binary_sensor.py
+++ b/homeassistant/components/threshold/binary_sensor.py
@@ -13,6 +13,7 @@ from homeassistant.const import (
     CONF_DEVICE_CLASS,
     CONF_ENTITY_ID,
     CONF_NAME,
+    STATE_UNAVAILABLE,
     STATE_UNKNOWN,
 )
 from homeassistant.core import callback
@@ -100,7 +101,9 @@ class ThresholdSensor(BinarySensorEntity):
 
             try:
                 self.sensor_value = (
-                    None if new_state.state == STATE_UNKNOWN else float(new_state.state)
+                    None
+                    if new_state.state in [STATE_UNKNOWN, STATE_UNAVAILABLE]
+                    else float(new_state.state)
                 )
             except (ValueError, TypeError):
                 self.sensor_value = None
diff --git a/tests/components/threshold/test_binary_sensor.py b/tests/components/threshold/test_binary_sensor.py
index af8c32a1549..b7c4a871068 100644
--- a/tests/components/threshold/test_binary_sensor.py
+++ b/tests/components/threshold/test_binary_sensor.py
@@ -1,6 +1,11 @@
 """The test for the threshold sensor platform."""
 
-from homeassistant.const import ATTR_UNIT_OF_MEASUREMENT, STATE_UNKNOWN, TEMP_CELSIUS
+from homeassistant.const import (
+    ATTR_UNIT_OF_MEASUREMENT,
+    STATE_UNAVAILABLE,
+    STATE_UNKNOWN,
+    TEMP_CELSIUS,
+)
 from homeassistant.setup import async_setup_component
 
 
@@ -283,7 +288,7 @@ async def test_sensor_in_range_with_hysteresis(hass):
     assert state.state == "on"
 
 
-async def test_sensor_in_range_unknown_state(hass):
+async def test_sensor_in_range_unknown_state(hass, caplog):
     """Test if source is within the range."""
     config = {
         "binary_sensor": {
@@ -322,6 +327,16 @@ async def test_sensor_in_range_unknown_state(hass):
     assert state.attributes.get("position") == "unknown"
     assert state.state == "off"
 
+    hass.states.async_set("sensor.test_monitored", STATE_UNAVAILABLE)
+    await hass.async_block_till_done()
+
+    state = hass.states.get("binary_sensor.threshold")
+
+    assert state.attributes.get("position") == "unknown"
+    assert state.state == "off"
+
+    assert "State is not numerical" not in caplog.text
+
 
 async def test_sensor_lower_zero_threshold(hass):
     """Test if a lower threshold of zero is set."""