From a053142601c2acf45845ed390ea5c465d6d93d00 Mon Sep 17 00:00:00 2001
From: jan iversen <jancasacondor@gmail.com>
Date: Mon, 1 Sep 2025 11:48:19 +0200
Subject: [PATCH] modbus: Do not modify registers (return wrong data).
 (#151131)

---
 homeassistant/components/modbus/entity.py |  5 ++-
 tests/components/modbus/test_sensor.py    | 40 +++++++++++++++++++++++
 2 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/homeassistant/components/modbus/entity.py b/homeassistant/components/modbus/entity.py
index 180495bd226a..d6101681d3f1 100644
--- a/homeassistant/components/modbus/entity.py
+++ b/homeassistant/components/modbus/entity.py
@@ -4,6 +4,7 @@ from __future__ import annotations
 
 from abc import abstractmethod
 from collections.abc import Callable
+import copy
 from datetime import datetime, timedelta
 import struct
 from typing import Any, cast
@@ -280,7 +281,9 @@ class BaseStructPlatform(BasePlatform, RestoreEntity):
         """Convert registers to proper result."""
 
         if self._swap:
-            registers = self._swap_registers(registers, self._slave_count)
+            registers = self._swap_registers(
+                copy.deepcopy(registers), self._slave_count
+            )
         byte_string = b"".join([x.to_bytes(2, byteorder="big") for x in registers])
         if self._data_type == DataType.STRING:
             return byte_string.decode()
diff --git a/tests/components/modbus/test_sensor.py b/tests/components/modbus/test_sensor.py
index 4910b4df0654..868e8a8baada 100644
--- a/tests/components/modbus/test_sensor.py
+++ b/tests/components/modbus/test_sensor.py
@@ -1357,6 +1357,46 @@ async def test_wrap_sensor(hass: HomeAssistant, mock_do_cycle, expected) -> None
     assert hass.states.get(ENTITY_ID).state == expected
 
 
+@pytest.mark.parametrize(
+    "do_config",
+    [
+        {
+            CONF_SENSORS: [
+                {
+                    CONF_NAME: TEST_ENTITY_NAME,
+                    CONF_ADDRESS: 201,
+                },
+            ],
+        },
+    ],
+)
+@pytest.mark.parametrize(
+    ("config_addon", "register_words", "expected"),
+    [
+        (
+            {
+                CONF_SWAP: CONF_SWAP_WORD,
+                CONF_DATA_TYPE: DataType.UINT32,
+            },
+            [0x0102, 0x0304],
+            "50594050",
+        ),
+    ],
+)
+async def test_wrap_regs_ok_sensor(
+    hass: HomeAssistant, mock_modbus_ha, mock_do_cycle, expected
+) -> None:
+    """Run test for sensor struct."""
+    assert hass.states.get(ENTITY_ID).state == expected
+    await hass.services.async_call(
+        HOMEASSISTANT_DOMAIN,
+        SERVICE_UPDATE_ENTITY,
+        {ATTR_ENTITY_ID: ENTITY_ID},
+        blocking=True,
+    )
+    assert hass.states.get(ENTITY_ID).state == expected
+
+
 @pytest.fixture(name="mock_restore")
 async def mock_restore(hass: HomeAssistant) -> None:
     """Mock restore cache."""