diff --git a/homeassistant/components/rainbird/__init__.py b/homeassistant/components/rainbird/__init__.py
index f9cd751a81e..e986cc302ae 100644
--- a/homeassistant/components/rainbird/__init__.py
+++ b/homeassistant/components/rainbird/__init__.py
@@ -218,6 +218,9 @@ def _async_fix_device_id(
     for device_entry in device_entries:
         unique_id = str(next(iter(device_entry.identifiers))[1])
         device_entry_map[unique_id] = device_entry
+        if unique_id.startswith(mac_address):
+            # Already in the correct format
+            continue
         if (suffix := unique_id.removeprefix(str(serial_number))) != unique_id:
             migrations[unique_id] = f"{mac_address}{suffix}"
 
diff --git a/tests/components/rainbird/test_init.py b/tests/components/rainbird/test_init.py
index 01e0c4458e4..520f8578c6e 100644
--- a/tests/components/rainbird/test_init.py
+++ b/tests/components/rainbird/test_init.py
@@ -449,3 +449,75 @@ async def test_fix_duplicate_device_ids(
     assert device_entry.identifiers == {(DOMAIN, MAC_ADDRESS_UNIQUE_ID)}
     assert device_entry.name_by_user == expected_device_name
     assert device_entry.disabled_by == expected_disabled_by
+
+
+async def test_reload_migration_with_leading_zero_mac(
+    hass: HomeAssistant,
+    device_registry: dr.DeviceRegistry,
+    entity_registry: er.EntityRegistry,
+) -> None:
+    """Test migration and reload of a device with a mac address with a leading zero."""
+    mac_address = "01:02:03:04:05:06"
+    mac_address_unique_id = dr.format_mac(mac_address)
+    serial_number = "0"
+
+    # Setup the config entry to be in a pre-migrated state
+    config_entry = MockConfigEntry(
+        domain=DOMAIN,
+        unique_id=serial_number,
+        data={
+            "host": "127.0.0.1",
+            "password": "password",
+            CONF_MAC: mac_address,
+            "serial_number": serial_number,
+        },
+    )
+    config_entry.add_to_hass(hass)
+
+    # Create a device and entity with the old unique id format
+    device_entry = device_registry.async_get_or_create(
+        config_entry_id=config_entry.entry_id,
+        identifiers={(DOMAIN, f"{serial_number}-1")},
+    )
+    entity_entry = entity_registry.async_get_or_create(
+        "switch",
+        DOMAIN,
+        f"{serial_number}-1-zone1",
+        suggested_object_id="zone1",
+        config_entry=config_entry,
+        device_id=device_entry.id,
+    )
+
+    # Setup the integration, which will migrate the unique ids
+    await hass.config_entries.async_setup(config_entry.entry_id)
+    await hass.async_block_till_done()
+
+    # Verify the device and entity were migrated to the new format
+    migrated_device_entry = device_registry.async_get_device(
+        identifiers={(DOMAIN, f"{mac_address_unique_id}-1")}
+    )
+    assert migrated_device_entry is not None
+    migrated_entity_entry = entity_registry.async_get(entity_entry.entity_id)
+    assert migrated_entity_entry is not None
+    assert migrated_entity_entry.unique_id == f"{mac_address_unique_id}-1-zone1"
+
+    # Reload the integration
+    await hass.config_entries.async_reload(config_entry.entry_id)
+    await hass.async_block_till_done()
+
+    # Verify the device and entity still have the correct identifiers and were not duplicated
+    reloaded_device_entry = device_registry.async_get(migrated_device_entry.id)
+    assert reloaded_device_entry is not None
+    assert reloaded_device_entry.identifiers == {(DOMAIN, f"{mac_address_unique_id}-1")}
+    reloaded_entity_entry = entity_registry.async_get(entity_entry.entity_id)
+    assert reloaded_entity_entry is not None
+    assert reloaded_entity_entry.unique_id == f"{mac_address_unique_id}-1-zone1"
+
+    assert (
+        len(dr.async_entries_for_config_entry(device_registry, config_entry.entry_id))
+        == 1
+    )
+    assert (
+        len(er.async_entries_for_config_entry(entity_registry, config_entry.entry_id))
+        == 1
+    )