From cdb7b9cc25d10eb67bcc6fcd8023cc0b80abc8a3 Mon Sep 17 00:00:00 2001
From: Rene Nulsch <33263735+ReneNulschDE@users.noreply.github.com>
Date: Tue, 23 Dec 2025 21:25:19 +0100
Subject: [PATCH] Fix ZeroDivisionError for inverse unit conversions (#159161)

---
 homeassistant/util/unit_conversion.py |  6 +++-
 tests/util/test_unit_conversion.py    | 52 +++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/homeassistant/util/unit_conversion.py b/homeassistant/util/unit_conversion.py
index b25895c3e8f..4593b0bd88c 100644
--- a/homeassistant/util/unit_conversion.py
+++ b/homeassistant/util/unit_conversion.py
@@ -154,7 +154,11 @@ class BaseUnitConverter:
             return lambda value: value
         from_ratio, to_ratio = cls._get_from_to_ratio(from_unit, to_unit)
         if cls._are_unit_inverses(from_unit, to_unit):
-            return lambda val: None if val is None else to_ratio / (val / from_ratio)
+            return (
+                lambda val: None
+                if val is None or val == 0
+                else to_ratio / (val / from_ratio)
+            )
         return lambda val: None if val is None else (val / from_ratio) * to_ratio
 
     @classmethod
diff --git a/tests/util/test_unit_conversion.py b/tests/util/test_unit_conversion.py
index 345c0bbfd51..95d970d14d7 100644
--- a/tests/util/test_unit_conversion.py
+++ b/tests/util/test_unit_conversion.py
@@ -1258,6 +1258,58 @@ def test_unit_conversion_factory_allow_none_with_none() -> None:
         )(None)
         is None
     )
+    assert (
+        EnergyDistanceConverter.converter_factory_allow_none(
+            UnitOfEnergyDistance.MILES_PER_KILO_WATT_HOUR,
+            UnitOfEnergyDistance.KILO_WATT_HOUR_PER_100_KM,
+        )(0)
+        is None
+    )
+    assert (
+        EnergyDistanceConverter.converter_factory_allow_none(
+            UnitOfEnergyDistance.KILO_WATT_HOUR_PER_100_KM,
+            UnitOfEnergyDistance.WATT_HOUR_PER_KM,
+        )(0)
+        == 0
+    )
+    assert (
+        EnergyDistanceConverter.converter_factory_allow_none(
+            UnitOfEnergyDistance.KM_PER_KILO_WATT_HOUR,
+            UnitOfEnergyDistance.MILES_PER_KILO_WATT_HOUR,
+        )(0.0)
+        == 0.0
+    )
+    assert (
+        EnergyDistanceConverter.converter_factory_allow_none(
+            UnitOfEnergyDistance.MILES_PER_KILO_WATT_HOUR,
+            UnitOfEnergyDistance.KM_PER_KILO_WATT_HOUR,
+        )(0)
+        == 0.0
+    )
+
+
+def test_unit_conversion_factory_allow_none_with_zero_for_inverse_units() -> None:
+    """Test converter_factory_allow_none returns None for zero with inverse units."""
+    # Test EnergyDistanceConverter with inverse units (kWh/100km <-> km/kWh)
+    assert (
+        EnergyDistanceConverter.converter_factory_allow_none(
+            UnitOfEnergyDistance.KILO_WATT_HOUR_PER_100_KM,
+            UnitOfEnergyDistance.KM_PER_KILO_WATT_HOUR,
+        )(0)
+        is None
+    )
+    assert (
+        EnergyDistanceConverter.converter_factory_allow_none(
+            UnitOfEnergyDistance.KM_PER_KILO_WATT_HOUR,
+            UnitOfEnergyDistance.KILO_WATT_HOUR_PER_100_KM,
+        )(0)
+        is None
+    )
+    # Test with non-zero value to ensure normal conversion still works
+    assert EnergyDistanceConverter.converter_factory_allow_none(
+        UnitOfEnergyDistance.KILO_WATT_HOUR_PER_100_KM,
+        UnitOfEnergyDistance.KM_PER_KILO_WATT_HOUR,
+    )(25) == pytest.approx(4)
 
 
 @pytest.mark.parametrize(