diff --git a/changelog.d/4818.bugfix b/changelog.d/4818.bugfix
new file mode 100644
index 0000000000..ebbc27a433
--- /dev/null
+++ b/changelog.d/4818.bugfix
@@ -0,0 +1 @@
+Fix bug where we didn't correctly throttle sending of USER_IP commands over replication.
diff --git a/synapse/replication/slave/storage/client_ips.py b/synapse/replication/slave/storage/client_ips.py
index 60641f1a49..5b8521c770 100644
--- a/synapse/replication/slave/storage/client_ips.py
+++ b/synapse/replication/slave/storage/client_ips.py
@@ -43,6 +43,8 @@ class SlavedClientIpStore(BaseSlavedStore):
         if last_seen is not None and (now - last_seen) < LAST_SEEN_GRANULARITY:
             return
 
+        self.client_ip_last_seen.prefill(key, now)
+
         self.hs.get_tcp_replication().send_user_ip(
             user_id, access_token, ip, user_agent, device_id, now
         )