diff --git a/patroni/postgresql/__init__.py b/patroni/postgresql/__init__.py
index 2b0a7c2a..13055dbe 100644
--- a/patroni/postgresql/__init__.py
+++ b/patroni/postgresql/__init__.py
@@ -109,10 +109,12 @@ class Postgresql(object):
         # Last known running process
         self._postmaster_proc = None
 
-        if self.is_running():
+        if self.is_running():  # we are "joining" already running postgres
             self.set_state('running')
             self.set_role('master' if self.is_leader() else 'replica')
-            self.config.write_postgresql_conf()  # we are "joining" already running postgres
+            # postpone writing postgresql.conf for 12+ because recovery parameters are not yet known
+            if self.major_version < 120000 or self.is_leader():
+                self.config.write_postgresql_conf()
             hba_saved = self.config.replace_pg_hba()
             ident_saved = self.config.replace_pg_ident()
             if hba_saved or ident_saved:
diff --git a/patroni/postgresql/config.py b/patroni/postgresql/config.py
index d0e5fc5b..c61a7695 100644
--- a/patroni/postgresql/config.py
+++ b/patroni/postgresql/config.py
@@ -702,7 +702,9 @@ class ConfigHandler(object):
         if wal_receiver_primary_slot_name is not None:
             self._current_recovery_params['primary_slot_name'][0] = wal_receiver_primary_slot_name
 
-        required = {'restart': 0, 'reload': 0}
+        # Increment the 'reload' to enforce write of postgresql.conf when joining the running postgres
+        required = {'restart': 0,
+                    'reload': int(not self._postgresql.cb_called and self._postgresql.major_version >= 120000)}
 
         def record_missmatch(mtype):
             required['restart' if mtype else 'reload'] += 1
diff --git a/tests/test_postgresql.py b/tests/test_postgresql.py
index 0fbc1b4d..54b5c674 100644
--- a/tests/test_postgresql.py
+++ b/tests/test_postgresql.py
@@ -224,6 +224,7 @@ class TestPostgresql(BaseTestPostgresql):
     @patch('patroni.postgresql.config.mtime', mock_mtime)
     @patch('patroni.postgresql.config.ConfigHandler._get_pg_settings')
     def test_check_recovery_conf(self, mock_get_pg_settings):
+        self.p.call_nowait('on_start')
         mock_get_pg_settings.return_value = {
             'primary_conninfo': ['primary_conninfo', 'foo=', None, 'string', 'postmaster', self.p.config._auto_conf],
             'recovery_min_apply_delay': ['recovery_min_apply_delay', '0', 'ms', 'integer', 'sighup', 'foo']
@@ -259,6 +260,7 @@ class TestPostgresql(BaseTestPostgresql):
     @patch.object(MockPostmaster, 'create_time', Mock(return_value=1234567), create=True)
     @patch('patroni.postgresql.config.ConfigHandler._get_pg_settings')
     def test__read_recovery_params(self, mock_get_pg_settings):
+        self.p.call_nowait('on_start')
         mock_get_pg_settings.return_value = {'primary_conninfo': ['primary_conninfo', '', None, 'string',
                                                                   'postmaster', self.p.config._postgresql_conf]}
         self.p.config.write_recovery_conf({'standby_mode': 'on', 'primary_conninfo': {'password': 'foo'}})