diff --git a/homeassistant/components/oncue/entity.py b/homeassistant/components/oncue/entity.py
index 40ca21edf96..d1942c532e7 100644
--- a/homeassistant/components/oncue/entity.py
+++ b/homeassistant/components/oncue/entity.py
@@ -3,6 +3,7 @@ from __future__ import annotations
 
 from aiooncue import OncueDevice, OncueSensor
 
+from homeassistant.const import ATTR_CONNECTIONS
 from homeassistant.helpers import device_registry as dr
 from homeassistant.helpers.entity import DeviceInfo, Entity, EntityDescription
 from homeassistant.helpers.update_coordinator import (
@@ -30,16 +31,21 @@ class OncueEntity(CoordinatorEntity, Entity):
         self._device_id = device_id
         self._attr_unique_id = f"{device_id}_{description.key}"
         self._attr_name = f"{device.name} {sensor.display_name}"
-        mac_address_hex = hex(int(device.sensors["MacAddress"].value))[2:]
         self._attr_device_info = DeviceInfo(
             identifiers={(DOMAIN, device_id)},
-            connections={(dr.CONNECTION_NETWORK_MAC, mac_address_hex)},
             name=device.name,
             hw_version=device.hardware_version,
             sw_version=device.sensors["FirmwareVersion"].display_value,
             model=device.sensors["GensetModelNumberSelect"].display_value,
             manufacturer="Kohler",
         )
+        try:
+            mac_address_hex = hex(int(device.sensors["MacAddress"].value))[2:]
+        except ValueError:  # MacAddress may be invalid if the gateway is offline
+            return
+        self._attr_device_info[ATTR_CONNECTIONS] = {
+            (dr.CONNECTION_NETWORK_MAC, mac_address_hex)
+        }
 
     @property
     def _oncue_value(self) -> str:
diff --git a/tests/components/oncue/__init__.py b/tests/components/oncue/__init__.py
index 48492a19933..32845aa8d26 100644
--- a/tests/components/oncue/__init__.py
+++ b/tests/components/oncue/__init__.py
@@ -269,6 +269,271 @@ MOCK_ASYNC_FETCH_ALL = {
 }
 
 
+MOCK_ASYNC_FETCH_ALL_OFFLINE_DEVICE = {
+    "456789": OncueDevice(
+        name="My Generator",
+        state="Off",
+        product_name="RDC 2.4",
+        hardware_version="319",
+        serial_number="SERIAL",
+        sensors={
+            "Product": OncueSensor(
+                name="Product",
+                display_name="Controller Type",
+                value="RDC 2.4",
+                display_value="RDC 2.4",
+                unit=None,
+            ),
+            "FirmwareVersion": OncueSensor(
+                name="FirmwareVersion",
+                display_name="Current Firmware",
+                value="2.0.6",
+                display_value="2.0.6",
+                unit=None,
+            ),
+            "LatestFirmware": OncueSensor(
+                name="LatestFirmware",
+                display_name="Latest Firmware",
+                value="2.0.6",
+                display_value="2.0.6",
+                unit=None,
+            ),
+            "EngineSpeed": OncueSensor(
+                name="EngineSpeed",
+                display_name="Engine Speed",
+                value="0",
+                display_value="0 R/min",
+                unit="R/min",
+            ),
+            "EngineTargetSpeed": OncueSensor(
+                name="EngineTargetSpeed",
+                display_name="Engine Target Speed",
+                value="0",
+                display_value="0 R/min",
+                unit="R/min",
+            ),
+            "EngineOilPressure": OncueSensor(
+                name="EngineOilPressure",
+                display_name="Engine Oil Pressure",
+                value=0,
+                display_value="0 Psi",
+                unit="Psi",
+            ),
+            "EngineCoolantTemperature": OncueSensor(
+                name="EngineCoolantTemperature",
+                display_name="Engine Coolant Temperature",
+                value=32,
+                display_value="32 F",
+                unit="F",
+            ),
+            "BatteryVoltage": OncueSensor(
+                name="BatteryVoltage",
+                display_name="Battery Voltage",
+                value="13.4",
+                display_value="13.4 V",
+                unit="V",
+            ),
+            "LubeOilTemperature": OncueSensor(
+                name="LubeOilTemperature",
+                display_name="Lube Oil Temperature",
+                value=32,
+                display_value="32 F",
+                unit="F",
+            ),
+            "GensetControllerTemperature": OncueSensor(
+                name="GensetControllerTemperature",
+                display_name="Generator Controller Temperature",
+                value=84.2,
+                display_value="84.2 F",
+                unit="F",
+            ),
+            "EngineCompartmentTemperature": OncueSensor(
+                name="EngineCompartmentTemperature",
+                display_name="Engine Compartment Temperature",
+                value=62.6,
+                display_value="62.6 F",
+                unit="F",
+            ),
+            "GeneratorTrueTotalPower": OncueSensor(
+                name="GeneratorTrueTotalPower",
+                display_name="Generator True Total Power",
+                value="0.0",
+                display_value="0.0 W",
+                unit="W",
+            ),
+            "GeneratorTruePercentOfRatedPower": OncueSensor(
+                name="GeneratorTruePercentOfRatedPower",
+                display_name="Generator True Percent Of Rated Power",
+                value="0",
+                display_value="0 %",
+                unit="%",
+            ),
+            "GeneratorVoltageAB": OncueSensor(
+                name="GeneratorVoltageAB",
+                display_name="Generator Voltage AB",
+                value="0.0",
+                display_value="0.0 V",
+                unit="V",
+            ),
+            "GeneratorVoltageAverageLineToLine": OncueSensor(
+                name="GeneratorVoltageAverageLineToLine",
+                display_name="Generator Voltage Average Line To Line",
+                value="0.0",
+                display_value="0.0 V",
+                unit="V",
+            ),
+            "GeneratorCurrentAverage": OncueSensor(
+                name="GeneratorCurrentAverage",
+                display_name="Generator Current Average",
+                value="0.0",
+                display_value="0.0 A",
+                unit="A",
+            ),
+            "GeneratorFrequency": OncueSensor(
+                name="GeneratorFrequency",
+                display_name="Generator Frequency",
+                value="0.0",
+                display_value="0.0 Hz",
+                unit="Hz",
+            ),
+            "GensetSerialNumber": OncueSensor(
+                name="GensetSerialNumber",
+                display_name="Generator Serial Number",
+                value="33FDGMFR0026",
+                display_value="33FDGMFR0026",
+                unit=None,
+            ),
+            "GensetState": OncueSensor(
+                name="GensetState",
+                display_name="Generator State",
+                value="Off",
+                display_value="Off",
+                unit=None,
+            ),
+            "GensetControllerSerialNumber": OncueSensor(
+                name="GensetControllerSerialNumber",
+                display_name="Generator Controller Serial Number",
+                value="-1",
+                display_value="-1",
+                unit=None,
+            ),
+            "GensetModelNumberSelect": OncueSensor(
+                name="GensetModelNumberSelect",
+                display_name="Genset Model Number Select",
+                value="38 RCLB",
+                display_value="38 RCLB",
+                unit=None,
+            ),
+            "GensetControllerClockTime": OncueSensor(
+                name="GensetControllerClockTime",
+                display_name="Generator Controller Clock Time",
+                value="2022-01-13 18:08:13",
+                display_value="2022-01-13 18:08:13",
+                unit=None,
+            ),
+            "GensetControllerTotalOperationTime": OncueSensor(
+                name="GensetControllerTotalOperationTime",
+                display_name="Generator Controller Total Operation Time",
+                value="16770.8",
+                display_value="16770.8 h",
+                unit="h",
+            ),
+            "EngineTotalRunTime": OncueSensor(
+                name="EngineTotalRunTime",
+                display_name="Engine Total Run Time",
+                value="28.1",
+                display_value="28.1 h",
+                unit="h",
+            ),
+            "EngineTotalRunTimeLoaded": OncueSensor(
+                name="EngineTotalRunTimeLoaded",
+                display_name="Engine Total Run Time Loaded",
+                value="5.5",
+                display_value="5.5 h",
+                unit="h",
+            ),
+            "EngineTotalNumberOfStarts": OncueSensor(
+                name="EngineTotalNumberOfStarts",
+                display_name="Engine Total Number Of Starts",
+                value="101",
+                display_value="101",
+                unit=None,
+            ),
+            "GensetTotalEnergy": OncueSensor(
+                name="GensetTotalEnergy",
+                display_name="Genset Total Energy",
+                value="1.2022309E7",
+                display_value="1.2022309E7 kWh",
+                unit="kWh",
+            ),
+            "AtsContactorPosition": OncueSensor(
+                name="AtsContactorPosition",
+                display_name="Ats Contactor Position",
+                value="Source1",
+                display_value="Source1",
+                unit=None,
+            ),
+            "AtsSourcesAvailable": OncueSensor(
+                name="AtsSourcesAvailable",
+                display_name="Ats Sources Available",
+                value="Source1",
+                display_value="Source1",
+                unit=None,
+            ),
+            "Source1VoltageAverageLineToLine": OncueSensor(
+                name="Source1VoltageAverageLineToLine",
+                display_name="Source1 Voltage Average Line To Line",
+                value="253.5",
+                display_value="253.5 V",
+                unit="V",
+            ),
+            "Source2VoltageAverageLineToLine": OncueSensor(
+                name="Source2VoltageAverageLineToLine",
+                display_name="Source2 Voltage Average Line To Line",
+                value="0.0",
+                display_value="0.0 V",
+                unit="V",
+            ),
+            "IPAddress": OncueSensor(
+                name="IPAddress",
+                display_name="IP Address",
+                value="1.2.3.4:1026",
+                display_value="1.2.3.4:1026",
+                unit=None,
+            ),
+            "MacAddress": OncueSensor(
+                name="MacAddress",
+                display_name="Mac Address",
+                value="--",
+                display_value="--",
+                unit=None,
+            ),
+            "ConnectedServerIPAddress": OncueSensor(
+                name="ConnectedServerIPAddress",
+                display_name="Connected Server IP Address",
+                value="40.117.195.28",
+                display_value="40.117.195.28",
+                unit=None,
+            ),
+            "NetworkConnectionEstablished": OncueSensor(
+                name="NetworkConnectionEstablished",
+                display_name="Network Connection Established",
+                value="true",
+                display_value="True",
+                unit=None,
+            ),
+            "SerialNumber": OncueSensor(
+                name="SerialNumber",
+                display_name="Serial Number",
+                value="1073879692",
+                display_value="1073879692",
+                unit=None,
+            ),
+        },
+    )
+}
+
+
 def _patch_login_and_data():
     @contextmanager
     def _patcher():
@@ -279,3 +544,15 @@ def _patch_login_and_data():
             yield
 
     return _patcher()
+
+
+def _patch_login_and_data_offline_device():
+    @contextmanager
+    def _patcher():
+        with patch("homeassistant.components.oncue.Oncue.async_login",), patch(
+            "homeassistant.components.oncue.Oncue.async_fetch_all",
+            return_value=MOCK_ASYNC_FETCH_ALL_OFFLINE_DEVICE,
+        ):
+            yield
+
+    return _patcher()
diff --git a/tests/components/oncue/test_sensor.py b/tests/components/oncue/test_sensor.py
index 5fe8b807c1b..60c9f68f81b 100644
--- a/tests/components/oncue/test_sensor.py
+++ b/tests/components/oncue/test_sensor.py
@@ -1,19 +1,29 @@
 """Tests for the oncue sensor."""
 from __future__ import annotations
 
+import pytest
+
 from homeassistant.components import oncue
 from homeassistant.components.oncue.const import DOMAIN
 from homeassistant.config_entries import ConfigEntryState
 from homeassistant.const import CONF_PASSWORD, CONF_USERNAME
 from homeassistant.core import HomeAssistant
+from homeassistant.helpers import device_registry as dr, entity_registry as er
 from homeassistant.setup import async_setup_component
 
-from . import _patch_login_and_data
+from . import _patch_login_and_data, _patch_login_and_data_offline_device
 
 from tests.common import MockConfigEntry
 
 
-async def test_sensors(hass: HomeAssistant) -> None:
+@pytest.mark.parametrize(
+    "patcher, connections",
+    [
+        [_patch_login_and_data, {("mac", "c9:24:22:6f:14:00")}],
+        [_patch_login_and_data_offline_device, set()],
+    ],
+)
+async def test_sensors(hass: HomeAssistant, patcher, connections) -> None:
     """Test that the sensors are setup with the expected values."""
     config_entry = MockConfigEntry(
         domain=DOMAIN,
@@ -21,11 +31,17 @@ async def test_sensors(hass: HomeAssistant) -> None:
         unique_id="any",
     )
     config_entry.add_to_hass(hass)
-    with _patch_login_and_data():
+    with patcher():
         await async_setup_component(hass, oncue.DOMAIN, {oncue.DOMAIN: {}})
         await hass.async_block_till_done()
     assert config_entry.state == ConfigEntryState.LOADED
 
+    entity_registry = er.async_get(hass)
+    ent = entity_registry.async_get("sensor.my_generator_latest_firmware")
+    device_registry = dr.async_get(hass)
+    dev = device_registry.async_get(ent.device_id)
+    assert dev.connections == connections
+
     assert len(hass.states.async_all("sensor")) == 25
     assert hass.states.get("sensor.my_generator_latest_firmware").state == "2.0.6"