diff --git a/homeassistant/components/emonitor/config_flow.py b/homeassistant/components/emonitor/config_flow.py
index bb18f03e3af..bd5650d28cd 100644
--- a/homeassistant/components/emonitor/config_flow.py
+++ b/homeassistant/components/emonitor/config_flow.py
@@ -12,7 +12,7 @@ from homeassistant.helpers import aiohttp_client
 from homeassistant.helpers.device_registry import format_mac
 
 from . import name_short_mac
-from .const import DOMAIN  # pylint:disable=unused-import
+from .const import DOMAIN
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -52,6 +52,7 @@ class ConfigFlow(config_entries.ConfigFlow, domain=DOMAIN):
                 await self.async_set_unique_id(
                     format_mac(info["mac_address"]), raise_on_progress=False
                 )
+                self._abort_if_unique_id_configured()
                 return self.async_create_entry(title=info["title"], data=user_input)
 
         return self.async_show_form(
diff --git a/tests/components/emonitor/test_config_flow.py b/tests/components/emonitor/test_config_flow.py
index 65fc471786f..1d71275409a 100644
--- a/tests/components/emonitor/test_config_flow.py
+++ b/tests/components/emonitor/test_config_flow.py
@@ -185,3 +185,39 @@ async def test_dhcp_already_exists(hass):
         await hass.async_block_till_done()
 
     assert result["type"] == "abort"
+    assert result["reason"] == "already_configured"
+
+
+async def test_user_unique_id_already_exists(hass):
+    """Test creating an entry where the unique_id already exists."""
+    await setup.async_setup_component(hass, "persistent_notification", {})
+    entry = MockConfigEntry(
+        domain=DOMAIN,
+        data={CONF_HOST: "1.2.3.4"},
+        unique_id="aa:bb:cc:dd:ee:ff",
+    )
+    entry.add_to_hass(hass)
+
+    result = await hass.config_entries.flow.async_init(
+        DOMAIN, context={"source": config_entries.SOURCE_USER}
+    )
+    assert result["type"] == "form"
+    assert result["errors"] == {}
+
+    with patch(
+        "homeassistant.components.emonitor.config_flow.Emonitor.async_get_status",
+        return_value=_mock_emonitor(),
+    ), patch(
+        "homeassistant.components.emonitor.async_setup_entry",
+        return_value=True,
+    ):
+        result2 = await hass.config_entries.flow.async_configure(
+            result["flow_id"],
+            {
+                "host": "1.2.3.4",
+            },
+        )
+        await hass.async_block_till_done()
+
+    assert result2["type"] == "abort"
+    assert result2["reason"] == "already_configured"