diff --git a/arcade/gui/property.py b/arcade/gui/property.py
index 542f753c5..4668aba87 100644
--- a/arcade/gui/property.py
+++ b/arcade/gui/property.py
@@ -403,9 +403,15 @@ def setdefault(self, *args):
             return dict.setdefault(self, *args)
 
     @override
-    def update(self, *args):
+    def update(self, /, *args, **kwargs):
         with self._dispatch():
-            dict.update(self, *args)
+            dict.update(self, *args, **kwargs)
+
+    @override
+    def __ior__(self, other):
+        with self._dispatch():
+            dict.__ior__(self, other)
+        return self
 
 
 K = TypeVar("K")
diff --git a/tests/unit/gui/test_property_dict_merges.py b/tests/unit/gui/test_property_dict_merges.py
new file mode 100644
index 000000000..df7f3e171
--- /dev/null
+++ b/tests/unit/gui/test_property_dict_merges.py
@@ -0,0 +1,98 @@
+import pytest
+
+from arcade.gui import DictProperty, bind
+
+
+class DictHolder:
+    values = DictProperty()
+
+
+def observe(holder):
+    notifications = []
+
+    def changed(instance, value, old_value):
+        notifications.append((id(instance), dict(value), dict(old_value)))
+
+    bind(holder, "values", changed)
+    return notifications
+
+
+@pytest.mark.parametrize(
+    ("args", "kwargs", "updates"),
+    [
+        ((), {"score": 2}, {"score": 2}),
+        (({"score": 2},), {"overlap": 3}, {"score": 2, "overlap": 3}),
+        (
+            ([("score", 2), ("overlap", 3)],),
+            {"overlap": 4},
+            {"score": 2, "overlap": 4},
+        ),
+        ((), {"self": 2}, {"self": 2}),
+        ((), {"args": 2, "kwargs": 3}, {"args": 2, "kwargs": 3}),
+        (({"score": 2},), {}, {"score": 2}),
+        ((), {}, {}),
+    ],
+)
+def test_update_accepts_dict_merge_forms_and_notifies_once(args, kwargs, updates):
+    holder = DictHolder()
+    original = {"existing": 1, "overlap": 0}
+    holder.values = original
+    alias = holder.values
+    notifications = observe(holder)
+
+    result = holder.values.update(*args, **kwargs)
+
+    expected = {**original, **updates}
+    assert result is None
+    assert holder.values is alias
+    assert holder.values == expected
+    assert notifications == [(id(holder), expected, original)]
+    assert original == {"existing": 1, "overlap": 0}
+
+
+@pytest.mark.parametrize("through_property", [False, True])
+@pytest.mark.parametrize("source_type", [dict, list, iter])
+def test_inplace_union_preserves_identity_and_notifies_once(through_property, source_type):
+    holder = DictHolder()
+    original = {"existing": 1, "overlap": 0}
+    holder.values = original
+    alias = holder.values
+    notifications = observe(holder)
+    source = source_type([("score", 2), ("existing", 5)])
+
+    if through_property:
+        holder.values |= source
+    else:
+        alias |= source
+
+    expected = {"existing": 5, "overlap": 0, "score": 2}
+    assert holder.values is alias
+    assert holder.values == expected
+    assert notifications == [(id(holder), expected, original)]
+    assert original == {"existing": 1, "overlap": 0}
+
+
+def test_nonmutating_union_does_not_notify():
+    holder = DictHolder()
+    holder.values = {"existing": 1}
+    notifications = observe(holder)
+
+    right = holder.values | {"score": 2}
+    left = {"score": 2} | holder.values
+
+    assert right == left == {"existing": 1, "score": 2}
+    assert type(right) is type(left) is dict
+    assert holder.values == {"existing": 1}
+    assert notifications == []
+
+
+def test_invalid_update_does_not_change_or_notify():
+    holder = DictHolder()
+    holder.values = {"existing": 1}
+    notifications = observe(holder)
+
+    with pytest.raises(TypeError):
+        holder.values.update(object(), score=2)
+
+    assert holder.values == {"existing": 1}
+    assert notifications == []