diff --git a/homeassistant/util/unit_system.py b/homeassistant/util/unit_system.py
index 8dad108ccbe..7e70f59e90d 100644
--- a/homeassistant/util/unit_system.py
+++ b/homeassistant/util/unit_system.py
@@ -215,9 +215,7 @@ def get_unit_system(key: str) -> UnitSystem:
     """Get unit system based on key."""
     if key == _CONF_UNIT_SYSTEM_IMPERIAL:
         return IMPERIAL_SYSTEM
-    if key == _CONF_UNIT_SYSTEM_METRIC:
-        return METRIC_SYSTEM
-    raise ValueError(f"`{key}` is not a valid unit system key")
+    return METRIC_SYSTEM
 
 
 validate_unit_system = vol.All(
diff --git a/tests/util/test_unit_system.py b/tests/util/test_unit_system.py
index 3019d6d0ff6..713685c6ac8 100644
--- a/tests/util/test_unit_system.py
+++ b/tests/util/test_unit_system.py
@@ -342,15 +342,11 @@ def test_deprecated_name(
     [
         (_CONF_UNIT_SYSTEM_METRIC, METRIC_SYSTEM),
         (_CONF_UNIT_SYSTEM_IMPERIAL, IMPERIAL_SYSTEM),
+        (None, METRIC_SYSTEM),
+        ("", METRIC_SYSTEM),
+        ("unknown_system", METRIC_SYSTEM),
     ],
 )
 def test_get_unit_system(key: str, expected_system: UnitSystem) -> None:
     """Test get_unit_system."""
     assert get_unit_system(key) is expected_system
-
-
-@pytest.mark.parametrize("key", [None, "", "invalid_custom"])
-def test_get_unit_system_invalid(key: str) -> None:
-    """Test get_unit_system with an invalid key."""
-    with pytest.raises(ValueError, match=f"`{key}` is not a valid unit system key"):
-        _ = get_unit_system(key)