diff --git a/bigchaindb/backend/localmongodb/query.py b/bigchaindb/backend/localmongodb/query.py
index 91673432..4f56dd73 100644
--- a/bigchaindb/backend/localmongodb/query.py
+++ b/bigchaindb/backend/localmongodb/query.py
@@ -9,7 +9,6 @@ from bigchaindb.backend.utils import module_dispatch_registrar
 from bigchaindb.backend.localmongodb.connection import LocalMongoDBConnection
 from bigchaindb.common.transaction import Transaction
 
-
 register_query = module_dispatch_registrar(backend.query)
 
 
diff --git a/bigchaindb/lib.py b/bigchaindb/lib.py
index f8f5777d..13d1ab71 100644
--- a/bigchaindb/lib.py
+++ b/bigchaindb/lib.py
@@ -479,6 +479,10 @@ class BigchainDB(object):
         return backend.query.store_pre_commit_state(self.connection, state)
 
     def store_validator_set(self, height, validators):
+        """Store validator set at a given `height`.
+           NOTE: If the validator set already exists at that `height` then an
+           exception will be raised.
+        """
         return backend.query.store_validator_set(self.connection, {'height': height,
                                                                    'validators': validators})