diff --git a/CHANGELOG.md b/CHANGELOG.md
index 827b77ca6..71f7d9766 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@
 
 ## Ongoing
 
+- PR [400](https://github.com/plugwise/python-plugwise-usb/pull/400): Fix for Issue [#399](https://github.com/plugwise/python-plugwise-usb/issues/399)
 - Test/validate for Python 3.14
 
 ## v0.47.1 - 2025-09-27
diff --git a/plugwise_usb/nodes/circle.py b/plugwise_usb/nodes/circle.py
index 1ff06fb92..833c3f8c3 100644
--- a/plugwise_usb/nodes/circle.py
+++ b/plugwise_usb/nodes/circle.py
@@ -880,9 +880,9 @@ async def clock_synchronize(self) -> bool:
             return False
 
         dt_now = datetime.now(tz=UTC)
-        days_diff = (response.day_of_week.value - dt_now.weekday()) % 7
-        circle_timestamp: datetime = dt_now.replace(
-            day=dt_now.day + days_diff,
+        days_diff = response.day_of_week.value - dt_now.weekday()
+        target_date = dt_now + timedelta(days=days_diff)
+        circle_timestamp = target_date.replace(
             hour=response.time.value.hour,
             minute=response.time.value.minute,
             second=response.time.value.second,
diff --git a/tests/stick_test_data.py b/tests/stick_test_data.py
index b70ca5239..1b1a18f39 100644
--- a/tests/stick_test_data.py
+++ b/tests/stick_test_data.py
@@ -609,6 +609,11 @@
         b"000000C1",  # Success ack
         b"0000" + b"00D7" + b"0098765432101234",  # msg_id, clock_ack, mac
     ),
+    b"\x05\x05\x03\x0300281111111111111111003010053101261F3D\r\n": (
+        "Circle+ Realtime set clock at month-end for 1111111111111111",
+        b"000000C1",  # Success ack
+        b"0000" + b"00D7" + b"1111111111111111",  # msg_id, clock_ack, mac
+    ),
     b"\x05\x05\x03\x03003E11111111111111111B8A\r\n": (
         "clock for 0011111111111111",
         b"000000C1",  # Success ack
diff --git a/tests/test_usb.py b/tests/test_usb.py
index 7de3159ab..b8a6e94fc 100644
--- a/tests/test_usb.py
+++ b/tests/test_usb.py
@@ -3039,3 +3039,42 @@ def fake_cache_bool(dummy: object, setting: str) -> bool | None:
         with patch("aiofiles.threadpool.sync_open", return_value=mock_file_stream):
             await stick.disconnect()
         await asyncio.sleep(1)
+
+    @freeze_time("2026-01-31 10:30:00", real_asyncio=True)
+    @pytest.mark.asyncio
+    async def test_clock_synchronize_month_overflow(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """Test clock_synchronize handles month-end date rollover correctly.
+
+        Regression test for issue `#399`: ensures that when the Circle's day_of_week
+        differs from the current weekday near month-end, the date calculation
+        doesn't attempt an invalid day value (e.g., Jan 32).
+        """
+        mock_serial = MockSerial(None)
+        monkeypatch.setattr(
+            pw_connection_manager,
+            "create_serial_connection",
+            mock_serial.mock_connection,
+        )
+        monkeypatch.setattr(pw_sender, "STICK_TIME_OUT", 0.2)
+        monkeypatch.setattr(pw_requests, "NODE_TIME_OUT", 2.0)
+
+        stick = pw_stick.Stick("test_port", cache_enabled=False)
+        await stick.connect()
+        await stick.initialize()
+        await stick.discover_nodes(load=False)
+        await self._wait_for_scan(stick)
+
+        # Get a Circle node
+        circle = stick.nodes.get("1111111111111111")
+        assert circle is not None
+        result = True
+        try:
+            await circle.load()
+        except ValueError:
+            result = False
+
+        assert result
+
+        await stick.disconnect()