diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index cc6035c838..7902d9ed6f 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -315,7 +315,7 @@ redaction_retention_period: 7d
 
 # How long to track users' last seen time and IPs in the database.
 #
-# Defaults to `28d`. Set to `null` to disable.
+# Defaults to `28d`. Set to `null` to disable clearing out of old rows.
 #
 #user_ips_max_age: 14d
 
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 655e7487a4..f8b7b4bef9 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -745,7 +745,7 @@ class ServerConfig(Config):
 
         # How long to track users' last seen time and IPs in the database.
         #
-        # Defaults to `28d`. Set to `null` to disable.
+        # Defaults to `28d`. Set to `null` to disable clearing out of old rows.
         #
         #user_ips_max_age: 14d
         """
diff --git a/synapse/storage/background_updates.py b/synapse/storage/background_updates.py
index 3fc25cd828..30788137a8 100644
--- a/synapse/storage/background_updates.py
+++ b/synapse/storage/background_updates.py
@@ -148,11 +148,8 @@ class BackgroundUpdateStore(SQLBaseStore):
 
         return False
 
-    async def has_completed_background_update(self, update_name):
+    async def has_completed_background_update(self, update_name) -> bool:
         """Check if the given background update has finished running.
-
-        Returns:
-            Deferred[bool]
         """
 
         if self._all_done:
diff --git a/synapse/storage/client_ips.py b/synapse/storage/client_ips.py
index 176c812b1f..a4d40dfa1e 100644
--- a/synapse/storage/client_ips.py
+++ b/synapse/storage/client_ips.py
@@ -506,7 +506,7 @@ class ClientIpStore(background_updates.BackgroundUpdateStore):
         """Removes entries in user IPs older than the configured period.
         """
 
-        if not self.user_ips_max_age:
+        if self.user_ips_max_age is None:
             # Nothing to do
             return