diff --git a/firestore/google/cloud/firestore_v1/_helpers.py b/firestore/google/cloud/firestore_v1/_helpers.py
index 7f47e74bcf18..09f5d7f41c0e 100644
--- a/firestore/google/cloud/firestore_v1/_helpers.py
+++ b/firestore/google/cloud/firestore_v1/_helpers.py
@@ -836,10 +836,6 @@ def _get_update_mask(self, allow_empty_mask=False):
         for field_path in self.top_level_paths:
             if field_path not in self.transform_paths:
                 mask_paths.append(field_path.to_api_repr())
-            else:
-                prefix = FieldPath(*field_path.parts[:-1])
-                if prefix.parts:
-                    mask_paths.append(prefix.to_api_repr())
 
         return common_pb2.DocumentMask(field_paths=mask_paths)
 
diff --git a/firestore/tests/system.py b/firestore/tests/system.py
index a8e683629add..f64f2fb9c5b5 100644
--- a/firestore/tests/system.py
+++ b/firestore/tests/system.py
@@ -223,6 +223,38 @@ def test_document_set_merge(client, cleanup):
     assert snapshot2.update_time == write_result2.update_time
 
 
+def test_document_set_merge_w_server_timestamp(client, cleanup):
+    document_id = "for-set" + unique_resource_id("-")
+    document = client.document("i-did-it", document_id)
+    # Add to clean-up before API request (in case ``set()`` fails).
+    cleanup(document)
+
+    # 0. Make sure the document doesn't exist yet
+    snapshot = document.get()
+    assert not snapshot.exists
+
+    # 1. Use ``create()`` to create the document.
+    data1 = {"name": "Sam", "address": {"city": "SF", "state": "CA"}}
+    write_result1 = document.create(data1)
+    snapshot1 = document.get()
+    assert snapshot1.update_time == write_result1.update_time
+
+    # 2. Call ``set()`` to merge
+    data2 = {"address": {"city": "LA"}, "now": firestore.SERVER_TIMESTAMP}
+    write_result2 = document.set(data2, merge=True)
+    snapshot2 = document.get()
+    stored_data = snapshot2.to_dict()
+    server_now = stored_data["now"]
+    assert stored_data == {
+        "name": "Sam",
+        "address": {"city": "LA", "state": "CA"},
+        "now": server_now,
+    }
+    # Make sure the create time hasn't changed.
+    assert snapshot2.create_time == snapshot1.create_time
+    assert snapshot2.update_time == write_result2.update_time
+
+
 def test_document_set_w_int_field(client, cleanup):
     document_id = "set-int-key" + unique_resource_id("-")
     document = client.document("i-did-it", document_id)
@@ -333,6 +365,30 @@ def test_update_document(client, cleanup):
         document.update({"bad": "time-future"}, option=option6)
 
 
+def test_update_document_w_server_timestamp(client, cleanup):
+    document_id = "for-update" + unique_resource_id("-")
+    document = client.document("made", document_id)
+    # Add to clean-up before API request (in case ``create()`` fails).
+    cleanup(document)
+
+    # 1. Update and create the document (with an option).
+    data = {"foo": {"bar": "baz"}, "scoop": {"barn": 981}, "other": True}
+    write_result2 = document.create(data)
+
+    # 2. Send an update without a field path (no option).
+    field_updates3 = {"foo.now": firestore.SERVER_TIMESTAMP}
+    write_result3 = document.update(field_updates3)
+    assert_timestamp_less(write_result2.update_time, write_result3.update_time)
+    snapshot3 = document.get()
+    stored_data = snapshot3.to_dict()
+    expected3 = {
+        "foo": stored_data["foo"],
+        "scoop": data["scoop"],
+        "other": data["other"],
+    }
+    assert stored_data == expected3
+
+
 def check_snapshot(snapshot, document, data, write_result):
     assert snapshot.reference is document
     assert snapshot.to_dict() == data
diff --git a/firestore/tests/unit/v1/test__helpers.py b/firestore/tests/unit/v1/test__helpers.py
index e33a2c9d0855..81338a0c359f 100644
--- a/firestore/tests/unit/v1/test__helpers.py
+++ b/firestore/tests/unit/v1/test__helpers.py
@@ -1951,7 +1951,6 @@ def test_with_merge_true_w_transform(self):
         document_data["butter"] = SERVER_TIMESTAMP
 
         write_pbs = self._call_fut(document_path, document_data, merge=True)
-
         update_pb = self._make_write_w_document(document_path, **update_data)
         self._update_document_mask(update_pb, field_paths=sorted(update_data))
         transform_pb = self._make_write_w_transform(document_path, fields=["butter"])
@@ -1987,7 +1986,6 @@ def test_with_merge_field_w_transform_masking_simple(self):
         document_data["butter"] = {"pecan": SERVER_TIMESTAMP}
 
         write_pbs = self._call_fut(document_path, document_data, merge=["butter.pecan"])
-
         update_pb = self._make_write_w_document(document_path)
         transform_pb = self._make_write_w_transform(
             document_path, fields=["butter.pecan"]
@@ -2107,14 +2105,8 @@ def _helper(self, option=None, do_transform=False, **write_kwargs):
             field_updates[field_path2] = SERVER_TIMESTAMP
 
         write_pbs = self._call_fut(document_path, field_updates, option)
-
         map_pb = document_pb2.MapValue(fields={"yum": _value_pb(bytes_value=value)})
-
-        if do_transform:
-            field_paths = [field_path1, "blog"]
-        else:
-            field_paths = [field_path1]
-
+        field_paths = [field_path1]
         expected_update_pb = write_pb2.Write(
             update=document_pb2.Document(
                 name=document_path, fields={"bitez": _value_pb(map_value=map_pb)}