diff --git a/patroni/postgresql/sync.py b/patroni/postgresql/sync.py
index b503af43..067583d7 100644
--- a/patroni/postgresql/sync.py
+++ b/patroni/postgresql/sync.py
@@ -159,8 +159,8 @@ class _SyncState(NamedTuple):
     :ivar sync_type: possible values: ``off``, ``priority``, ``quorum``
     :ivar numsync: how many nodes are required to be synchronous (according to ``synchronous_standby_names``).
                    Is ``0`` if ``synchronous_standby_names`` value is invalid or contains ``*``.
-    :ivar numsync_confirmed: how many nodes are known to be synchronous according to the ``pg_stat_replication``
-                             view. Only nodes that caught up with the :attr:`SyncHandler._primary_flush_lsn` are counted.
+    :ivar numsync_confirmed: how many nodes are known to be synchronous according to the ``pg_stat_replication`` view.
+                             Only nodes that caught up with the :attr:`SyncHandler._primary_flush_lsn` are counted.
     :ivar sync: collection of synchronous node names. In case of quorum commit all nodes listed
                 in ``synchronous_standby_names``, otherwise nodes that are confirmed to be synchronous according
                 to the ``pg_stat_replication`` view.
diff --git a/patroni/quorum.py b/patroni/quorum.py
index 2d75f0c0..c510cfca 100644
--- a/patroni/quorum.py
+++ b/patroni/quorum.py
@@ -1,8 +1,10 @@
+"""Implement state machine to manage ``synchronous_standby_names`` GUC and ``/sync`` key in DCS."""
 import logging
 
 from typing import Collection, Iterator, NamedTuple, Optional
 
 from .collections import CaseInsensitiveSet
+from .exceptions import PatroniException
 
 logger = logging.getLogger(__name__)
 
@@ -31,12 +33,12 @@ class Transition(NamedTuple):
     names: CaseInsensitiveSet
 
 
-class QuorumError(Exception):
+class QuorumError(PatroniException):
     """Exception indicating that the quorum state is broken."""
 
 
-class QuorumStateResolver(object):
-    """Calculates a list of state transition tuples of the form `('sync'/'quorum'/'restart',leader,number,set_of_names)`
+class QuorumStateResolver:
+    """Calculates a list of state transitions and yields them as :class:`Transition` named tuples.
 
     Synchronous replication state is set in two places:
 
@@ -142,6 +144,7 @@ class QuorumStateResolver(object):
 
         .. seealso::
             Check :class:`QuorumStateResolver`'s docstring for more information.
+
         :raises:
             :exc:`QuorumError`: in case of broken state"""
         voters = CaseInsensitiveSet(self.voters | CaseInsensitiveSet([self.leader]))