diff --git a/homeassistant/components/sensor/octoprint.py b/homeassistant/components/sensor/octoprint.py
index 4bf543f3831..f7e7fa30817 100644
--- a/homeassistant/components/sensor/octoprint.py
+++ b/homeassistant/components/sensor/octoprint.py
@@ -95,6 +95,9 @@ class OctoPrintSensor(Entity):
         """Return the state of the sensor."""
         sensor_unit = self.unit_of_measurement
         if sensor_unit == TEMP_CELSIUS or sensor_unit == "%":
+            # API sometimes returns null and not 0
+            if self._state is None:
+                self._state = 0
             return round(self._state, 2)
         else:
             return self._state