diff --git a/lib/charms/mongos/v0/upgrade_helpers.py b/lib/charms/mongos/v0/upgrade_helpers.py
index e0422656..25ad2fdd 100644
--- a/lib/charms/mongos/v0/upgrade_helpers.py
+++ b/lib/charms/mongos/v0/upgrade_helpers.py
@@ -32,7 +32,7 @@
 
 # Increment this PATCH version before using `charmcraft publish-lib` or reset
 # to 0 if you are raising the major API version
-LIBPATCH = 3
+LIBPATCH = 6
 
 logger = logging.getLogger(__name__)
 
@@ -319,10 +319,10 @@ def pre_upgrade_check(self) -> None:
         See https://chat.canonical.com/canonical/pl/cmf6uhm1rp8b7k8gkjkdsj4mya
         """
         # Until the mongos charm has a config-server there is nothing to check. Allow an upgrade.
-        if not self.charm.mongos_initialised:
+        if not self._charm.mongos_initialised:
             return
 
-        if not self.is_mongos_able_to_read_write():
+        if not self._charm.upgrade.is_mongos_able_to_read_write():
             raise PrecheckFailed("mongos is not able to read/write.")