diff --git a/homeassistant/components/mill/sensor.py b/homeassistant/components/mill/sensor.py
index f82d3dbcc34..44d08e828f3 100644
--- a/homeassistant/components/mill/sensor.py
+++ b/homeassistant/components/mill/sensor.py
@@ -14,12 +14,11 @@ from homeassistant.const import (
     CONCENTRATION_PARTS_PER_MILLION,
     CONF_USERNAME,
     ENERGY_KILO_WATT_HOUR,
-    ENTITY_CATEGORY_DIAGNOSTIC,
     PERCENTAGE,
     TEMP_CELSIUS,
 )
 from homeassistant.core import callback
-from homeassistant.helpers.entity import DeviceInfo
+from homeassistant.helpers.entity import DeviceInfo, EntityCategory
 from homeassistant.helpers.update_coordinator import CoordinatorEntity
 
 from .const import (
@@ -75,7 +74,7 @@ SENSOR_TYPES: tuple[SensorEntityDescription, ...] = (
         native_unit_of_measurement=PERCENTAGE,
         name="Battery",
         state_class=SensorStateClass.MEASUREMENT,
-        entity_category=ENTITY_CATEGORY_DIAGNOSTIC,
+        entity_category=EntityCategory.DIAGNOSTIC,
     ),
     SensorEntityDescription(
         key=ECO2,