diff --git a/homeassistant/components/mqtt/config_flow.py b/homeassistant/components/mqtt/config_flow.py
index b022a46cbe7..ee451b5f81d 100644
--- a/homeassistant/components/mqtt/config_flow.py
+++ b/homeassistant/components/mqtt/config_flow.py
@@ -2771,11 +2771,10 @@ class MQTTSubentryFlowHandler(ConfigSubentryFlow):
             reconfig=True,
         )
         if user_input is not None:
-            new_device_data, errors = validate_user_input(
-                user_input, MQTT_DEVICE_PLATFORM_FIELDS
-            )
-            if "mqtt_settings" in user_input:
-                new_device_data["mqtt_settings"] = user_input["mqtt_settings"]
+            new_device_data: dict[str, Any] = user_input.copy()
+            _, errors = validate_user_input(user_input, MQTT_DEVICE_PLATFORM_FIELDS)
+            if "advanced_settings" in new_device_data:
+                new_device_data |= new_device_data.pop("advanced_settings")
             if not errors:
                 self._subentry_data[CONF_DEVICE] = cast(MqttDeviceData, new_device_data)
                 if self.source == SOURCE_RECONFIGURE:
diff --git a/tests/components/mqtt/test_config_flow.py b/tests/components/mqtt/test_config_flow.py
index 12f77a95c48..9386f1da32c 100644
--- a/tests/components/mqtt/test_config_flow.py
+++ b/tests/components/mqtt/test_config_flow.py
@@ -4077,6 +4077,7 @@ async def test_subentry_reconfigure_update_device_properties(
             "model": "Beer bottle XL",
             "model_id": "bn003",
             "configuration_url": "https://example.com",
+            "mqtt_settings": {"qos": 1},
         },
     )
     assert result["type"] is FlowResultType.MENU
@@ -4090,12 +4091,15 @@ async def test_subentry_reconfigure_update_device_properties(
     assert result["type"] is FlowResultType.ABORT
     assert result["reason"] == "reconfigure_successful"
 
-    # Check our device was updated
+    # Check our device and mqtt data was updated correctly
     device = deepcopy(dict(subentry.data))["device"]
     assert device["name"] == "Beer notifier"
     assert "hw_version" not in device
     assert device["model"] == "Beer bottle XL"
     assert device["model_id"] == "bn003"
+    assert device["sw_version"] == "1.1"
+    assert device["mqtt_settings"]["qos"] == 1
+    assert "qos" not in device
 
 
 @pytest.mark.parametrize(