diff --git a/ops/model.py b/ops/model.py
index 7fa8f3027..3bafa88ab 100644
--- a/ops/model.py
+++ b/ops/model.py
@@ -91,16 +91,6 @@
 })
 
 
-# Copied from typeshed.
-_KT = typing.TypeVar("_KT")
-_VT_co = typing.TypeVar("_VT_co", covariant=True)
-
-
-class _SupportsKeysAndGetItem(typing.Protocol[_KT, _VT_co]):
-    def keys(self) -> typing.Iterable[_KT]: ...
-    def __getitem__(self, __key: _KT) -> _VT_co: ...
-
-
 logger = logging.getLogger(__name__)
 
 MAX_LOG_LINE_LEN = 131071  # Max length of strings to pass to subshell.
@@ -1722,7 +1712,7 @@ def __getitem__(self, key: str) -> str:
         self._validate_read()
         return super().__getitem__(key)
 
-    def update(self, other: _SupportsKeysAndGetItem[str, str], **kwargs: str):
+    def update(self, other: typing.Any = (), /, **kwargs: str):
         """Update the data from dict/iterable other and the kwargs."""
         super().update(other, **kwargs)
 
diff --git a/test/test_model.py b/test/test_model.py
index 1f7c212a2..2037585b1 100644
--- a/test/test_model.py
+++ b/test/test_model.py
@@ -232,6 +232,32 @@ def test_get_app_relation_data(self, harness: ops.testing.Harness[ops.CharmBase]
                 relation_id, harness.model.app) == harness.get_relation_data(
                 relation_id, local_app) == {'foo': 'bar'}
 
+    @pytest.mark.parametrize('args,kwargs', [
+        (({'foo': 'baz'}, ), {}),
+        (([('foo', 'baz')], ), {}),
+        ((), {'foo': 'baz'})
+    ])
+    def test_update_app_relation_data(
+        self,
+        args: typing.Tuple[typing.Any, ...],
+        kwargs: typing.Dict[str, str],
+        harness: ops.testing.Harness[ops.CharmBase],
+    ):
+        harness.set_leader(True)
+        harness.begin()
+        relation_id = harness.add_relation('db1', 'remote')
+        harness.add_relation_unit(relation_id, 'remote/0')
+        with harness._event_context('foo_event'):
+            harness.update_relation_data(
+                relation_id,
+                harness.model.app.name,
+                {'foo': 'bar'})
+            rel = harness.model.get_relation('db1', relation_id)
+            assert rel is not None
+            rel.data[harness.model.app].update(*args, **kwargs)
+            assert harness.get_relation_data(
+                relation_id, harness.model.app) == {'foo': 'baz'}
+
     def test_unit_relation_data(self, harness: ops.testing.Harness[ops.CharmBase]):
         relation_id = harness.add_relation('db1', 'remoteapp1')
         harness.add_relation_unit(relation_id, 'remoteapp1/0')