diff --git a/google/cloud/ndb/model.py b/google/cloud/ndb/model.py
index 4b7dd6f1..57691a76 100644
--- a/google/cloud/ndb/model.py
+++ b/google/cloud/ndb/model.py
@@ -4026,7 +4026,7 @@ def _to_base_type(self, value):
                 "Cannot convert to protocol buffer. Expected {} value; "
                 "received {}".format(self._model_class.__name__, value)
             )
-        return _entity_to_ds_entity(value)
+        return _entity_to_ds_entity(value, set_key=False)
 
     def _from_base_type(self, value):
         """Convert a value from the "base" value type for this property.
diff --git a/tests/system/test_misc.py b/tests/system/test_misc.py
new file mode 100644
index 00000000..eeb6d172
--- /dev/null
+++ b/tests/system/test_misc.py
@@ -0,0 +1,62 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""
+Difficult to classify regression tests.
+"""
+import pickle
+
+import pytest
+import six
+
+from google.cloud import ndb
+
+
+# Pickle can only pickle/unpickle global classes
+class PickleOtherKind(ndb.Model):
+    foo = ndb.IntegerProperty()
+
+    @classmethod
+    def _get_kind(cls):
+        return "OtherKind"
+
+
+class PickleSomeKind(ndb.Model):
+    other = ndb.StructuredProperty(PickleOtherKind)
+
+    @classmethod
+    def _get_kind(cls):
+        return "SomeKind"
+
+
+@pytest.mark.skipif(
+    six.PY2, reason="Pickling doesn't work in Python 2. See: Issue #311"
+)
+@pytest.mark.usefixtures("client_context")
+def test_pickle_roundtrip_structured_property(dispose_of):
+    """Regression test for Issue #281.
+
+    https://github.com/googleapis/python-ndb/issues/281
+    """
+    ndb.Model._kind_map["SomeKind"] = PickleSomeKind
+    ndb.Model._kind_map["OtherKind"] = PickleOtherKind
+
+    entity = PickleSomeKind(other=PickleOtherKind(foo=1))
+    key = entity.put()
+    dispose_of(key._key)
+
+    entity = key.get(use_cache=False)
+    assert entity.other.key is None or entity.other.key.id() is None
+    entity = pickle.loads(pickle.dumps(entity))
+    assert entity.other.foo == 1
diff --git a/tests/unit/test_model.py b/tests/unit/test_model.py
index c29d3733..6853b7eb 100644
--- a/tests/unit/test_model.py
+++ b/tests/unit/test_model.py
@@ -3320,7 +3320,7 @@ class MineToo(model.Model):
         ds_bar = MineToo.bar._to_base_type(minetoo.bar)
         assert isinstance(ds_bar, entity_module.Entity)
         assert ds_bar["foo"] == "bar"
-        assert ds_bar.kind == "Mine"
+        assert ds_bar.key is None
 
     @staticmethod
     @pytest.mark.usefixtures("in_context")