diff --git a/src/modules/account_registration.rs b/src/modules/account_registration.rs
index fbfafee..701d260 100644
--- a/src/modules/account_registration.rs
+++ b/src/modules/account_registration.rs
@@ -23,6 +23,7 @@ use std::collections::HashMap;
 
 use crate::command::{CmdResult, Command};
 use crate::http::{json_str, urlencode};
+use crate::module::Module;
 use crate::server::{now, Server};
 use crate::Uid;
 
@@ -30,6 +31,26 @@ use crate::Uid;
 #[derive(Default)]
 struct RateState(HashMap<String, Vec<u64>>);
 
+/// Ticks the rate-limit table: prunes each IP's timestamps to the window and drops
+/// IPs with none left, so the map can't accumulate one entry per distinct IP that
+/// ever issued a REGISTER over the process lifetime.
+pub struct AcctRegGc;
+impl Module for AcctRegGc {
+    fn name(&self) -> &'static str {
+        "account_registration"
+    }
+    fn on_tick(&mut self, s: &mut Server) {
+        let window = s.conf_num("acctregister_ratetime", 3600u64);
+        let n = now();
+        if let Some(st) = s.ext.get_mut::<RateState>() {
+            st.0.retain(|_, hist| {
+                hist.retain(|&t| n.saturating_sub(t) < window);
+                !hist.is_empty()
+            });
+        }
+    }
+}
+
 fn enabled(s: &Server) -> bool {
     s.conf_bool("account_registration", false) && s.conf("acctregister_registerurl").is_some()
 }
diff --git a/src/modules/mod.rs b/src/modules/mod.rs
index 148b796..8f8dbe9 100644
--- a/src/modules/mod.rs
+++ b/src/modules/mod.rs
@@ -112,6 +112,7 @@ pub fn default_modules() -> Vec<Box<dyn Module>> {
         Box::new(operprefix::OperPrefix),
         Box::new(permchannels::PermChannels::default()),
         Box::new(chathistory::ChatHistoryGc),
+        Box::new(account_registration::AcctRegGc),
     ]
 }