diff --git a/homeassistant/components/nut/__init__.py b/homeassistant/components/nut/__init__.py
index e9d6f41f8d8..3c67b28196a 100644
--- a/homeassistant/components/nut/__init__.py
+++ b/homeassistant/components/nut/__init__.py
@@ -121,6 +121,9 @@ async def async_setup_entry(hass: HomeAssistant, entry: NutConfigEntry) -> bool:
     if unique_id is None:
         unique_id = entry.entry_id
 
+    elif entry.unique_id is None:
+        hass.config_entries.async_update_entry(entry, unique_id=unique_id)
+
     if username is not None and password is not None:
         # Dynamically add outlet integration commands
         additional_integration_commands = set()
diff --git a/homeassistant/components/nut/config_flow.py b/homeassistant/components/nut/config_flow.py
index d1bbd209626..5996c1c0087 100644
--- a/homeassistant/components/nut/config_flow.py
+++ b/homeassistant/components/nut/config_flow.py
@@ -22,7 +22,7 @@ from homeassistant.core import HomeAssistant
 from homeassistant.data_entry_flow import AbortFlow
 from homeassistant.helpers.service_info.zeroconf import ZeroconfServiceInfo
 
-from . import PyNUTData
+from . import PyNUTData, _unique_id_from_status
 from .const import DEFAULT_HOST, DEFAULT_PORT, DOMAIN
 
 _LOGGER = logging.getLogger(__name__)
@@ -119,6 +119,11 @@ class NutConfigFlow(ConfigFlow, domain=DOMAIN):
 
                 if self._host_port_alias_already_configured(nut_config):
                     return self.async_abort(reason="already_configured")
+
+                if unique_id := _unique_id_from_status(info["available_resources"]):
+                    await self.async_set_unique_id(unique_id)
+                    self._abort_if_unique_id_configured()
+
                 title = _format_host_port_alias(nut_config)
                 return self.async_create_entry(title=title, data=nut_config)
 
@@ -141,8 +146,13 @@ class NutConfigFlow(ConfigFlow, domain=DOMAIN):
             self.nut_config.update(user_input)
             if self._host_port_alias_already_configured(nut_config):
                 return self.async_abort(reason="already_configured")
-            _, errors, placeholders = await self._async_validate_or_error(nut_config)
+
+            info, errors, placeholders = await self._async_validate_or_error(nut_config)
             if not errors:
+                if unique_id := _unique_id_from_status(info["available_resources"]):
+                    await self.async_set_unique_id(unique_id)
+                    self._abort_if_unique_id_configured()
+
                 title = _format_host_port_alias(nut_config)
                 return self.async_create_entry(title=title, data=nut_config)
 
diff --git a/tests/components/nut/test_config_flow.py b/tests/components/nut/test_config_flow.py
index e9bee23c4ce..6237ad341b4 100644
--- a/tests/components/nut/test_config_flow.py
+++ b/tests/components/nut/test_config_flow.py
@@ -20,7 +20,7 @@ from homeassistant.core import HomeAssistant
 from homeassistant.data_entry_flow import FlowResultType
 from homeassistant.helpers.service_info.zeroconf import ZeroconfServiceInfo
 
-from .util import _get_mock_nutclient
+from .util import _get_mock_nutclient, async_init_integration
 
 from tests.common import MockConfigEntry
 
@@ -524,6 +524,104 @@ async def test_abort_if_already_setup(hass: HomeAssistant) -> None:
         assert result2["reason"] == "already_configured"
 
 
+async def test_abort_duplicate_unique_ids(hass: HomeAssistant) -> None:
+    """Test we abort if unique_id is already setup."""
+
+    list_vars = {
+        "device.mfr": "Some manufacturer",
+        "device.model": "Some model",
+        "device.serial": "0000-1",
+    }
+    await async_init_integration(
+        hass,
+        list_ups={"ups1": "UPS 1"},
+        list_vars=list_vars,
+    )
+
+    mock_pynut = _get_mock_nutclient(list_ups={"ups2": "UPS 2"}, list_vars=list_vars)
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": config_entries.SOURCE_USER}
+    )
+
+    with patch(
+        "homeassistant.components.nut.AIONUTClient",
+        return_value=mock_pynut,
+    ):
+        result2 = await hass.config_entries.flow.async_configure(
+            result["flow_id"],
+            {
+                CONF_HOST: "1.1.1.1",
+                CONF_PORT: 2222,
+            },
+        )
+        await hass.async_block_till_done()
+
+        assert result2["type"] is FlowResultType.ABORT
+        assert result2["reason"] == "already_configured"
+
+
+async def test_abort_multiple_ups_duplicate_unique_ids(hass: HomeAssistant) -> None:
+    """Test we abort on multiple devices if unique_id is already setup."""
+
+    list_vars = {
+        "device.mfr": "Some manufacturer",
+        "device.model": "Some model",
+        "device.serial": "0000-1",
+    }
+
+    mock_pynut = _get_mock_nutclient(
+        list_ups={"ups2": "UPS 2", "ups3": "UPS 3"}, list_vars=list_vars
+    )
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": config_entries.SOURCE_USER}
+    )
+    assert result["type"] is FlowResultType.FORM
+    assert result["errors"] == {}
+
+    with patch(
+        "homeassistant.components.nut.AIONUTClient",
+        return_value=mock_pynut,
+    ):
+        result2 = await hass.config_entries.flow.async_configure(
+            result["flow_id"],
+            {
+                CONF_HOST: "1.1.1.1",
+                CONF_PORT: 2222,
+            },
+        )
+        await hass.async_block_till_done()
+
+        assert result2["step_id"] == "ups"
+        assert result2["type"] is FlowResultType.FORM
+
+    await async_init_integration(
+        hass,
+        list_ups={"ups1": "UPS 1"},
+        list_vars=list_vars,
+    )
+
+    with (
+        patch(
+            "homeassistant.components.nut.AIONUTClient",
+            return_value=mock_pynut,
+        ),
+        patch(
+            "homeassistant.components.nut.async_setup_entry",
+            return_value=True,
+        ),
+    ):
+        result3 = await hass.config_entries.flow.async_configure(
+            result["flow_id"],
+            {CONF_ALIAS: "ups2"},
+        )
+        await hass.async_block_till_done()
+
+        assert result3["type"] is FlowResultType.ABORT
+        assert result3["reason"] == "already_configured"
+
+
 async def test_abort_if_already_setup_alias(hass: HomeAssistant) -> None:
     """Test we abort if component is already setup with same alias."""
     config_entry = MockConfigEntry(