diff --git a/bigchaindb/backend/localmongodb/query.py b/bigchaindb/backend/localmongodb/query.py
index b7b21d8d..e6fe11ab 100644
--- a/bigchaindb/backend/localmongodb/query.py
+++ b/bigchaindb/backend/localmongodb/query.py
@@ -4,7 +4,6 @@ from pymongo import DESCENDING
 
 from bigchaindb import backend
 from bigchaindb.backend.exceptions import DuplicateKeyError
-from bigchaindb.common.exceptions import MultipleValidatorOperationError
 from bigchaindb.backend.utils import module_dispatch_registrar
 from bigchaindb.backend.localmongodb.connection import LocalMongoDBConnection
 from bigchaindb.common.transaction import Transaction
@@ -111,7 +110,8 @@ def get_spent(conn, transaction_id, output):
 def get_latest_block(conn):
     return conn.run(
         conn.collection('blocks')
-        .find_one(sort=[('height', DESCENDING)]))
+        .find_one(projection={'_id': False},
+                  sort=[('height', DESCENDING)]))
 
 
 @register_query(LocalMongoDBConnection)
@@ -281,9 +281,9 @@ def get_pre_commit_state(conn, commit_id):
 def store_validator_set(conn, validators_update):
     height = validators_update['height']
     return conn.run(
-        conn.collection('validators').update_one(
-            {"height": height},
-            {"$set": validators_update},
+        conn.collection('validators').replace_one(
+            {'height': height},
+            validators_update,
             upsert=True
         )
     )
diff --git a/bigchaindb/core.py b/bigchaindb/core.py
index bfcc97e9..08d3888a 100644
--- a/bigchaindb/core.py
+++ b/bigchaindb/core.py
@@ -136,8 +136,11 @@ class App(BaseApplication):
         # TODO: calculate if an election has concluded
         # NOTE: ensure the local validator set is updated
         validator_updates = self.bigchaindb.get_validator_update(self.block_transactions)
-        validator_set = new_validator_set(self.bigchaindb, self.new_height, validator_updates)
-        self.bigchaindb.store_validator_set(self.new_height+1, validator_set)
+
+        if validator_updates:
+            validator_set = new_validator_set(self.bigchaindb, self.new_height, validator_updates)
+            self.bigchaindb.store_validator_set(self.new_height+1, validator_set)
+
         validator_updates = [encode_validator(v) for v in validator_updates]
 
         # Store pre-commit state to recover in case there is a crash
@@ -197,7 +200,7 @@ def new_validator_set(bigchain, height, updates):
     updates_dict = {}
     for u in updates:
         updates_dict[u['public_key']] = {'pub_key': {'type': 'ed25519',
-                                                     'data': public_key_to_base64(u['public_key']) },
+                                                     'data': public_key_to_base64(u['public_key'])},
                                          'voting_power': u['power']}
     new_validators_dict = {**validators_dict, **updates_dict}
     return list(new_validators_dict.values())
diff --git a/tests/tendermint/test_integration.py b/tests/tendermint/test_integration.py
index d7de519f..35fe5074 100644
--- a/tests/tendermint/test_integration.py
+++ b/tests/tendermint/test_integration.py
@@ -7,7 +7,6 @@ import pytest
 
 from abci.server import ProtocolHandler
 from abci.encoding import read_messages
-from copy import deepcopy
 from io import BytesIO
 
 
diff --git a/tests/upsert_validator/test_validator_election_vote.py b/tests/upsert_validator/test_validator_election_vote.py
index ad77784f..185107db 100644
--- a/tests/upsert_validator/test_validator_election_vote.py
+++ b/tests/upsert_validator/test_validator_election_vote.py
@@ -218,25 +218,19 @@ def test_get_validator_update(b_mock, valid_election, ed25519_node_keys):
 
 @pytest.mark.abci
 def test_upsert_validator(b, node_key, node_keys, new_validator, ed25519_node_keys):
-    from bigchaindb.backend import connect
     from bigchaindb.tendermint_utils import public_key_to_base64
     import time
     import requests
 
-    conn = connect()
     (node_pub, _) = list(node_keys.items())[0]
 
     validators = [{'pub_key': {'type': 'ed25519',
                                'data': node_pub},
                    'voting_power': 10}]
 
+    latest_block = b.get_latest_block()
     # reset the validator set
-    conn.run(
-        conn.collection('validators').find_one_and_update(
-            {"height": 1},
-            {"$set": {"validators": validators}}
-        )
-    )
+    b.store_validator_set(latest_block['height'], validators)
 
     power = 1
     public_key = '9B3119650DF82B9A5D8A12E38953EA47475C09F0C48A4E6A0ECE182944B24403'