diff --git a/src/database/key_value/rooms/auth_chain.rs b/src/database/key_value/rooms/auth_chain.rs
index 1dacb470..435a1c03 100644
--- a/src/database/key_value/rooms/auth_chain.rs
+++ b/src/database/key_value/rooms/auth_chain.rs
@@ -1,9 +1,9 @@
-use std::{collections::HashSet, mem::size_of, sync::Arc};
+use std::{mem::size_of, sync::Arc};
 
 use crate::{database::KeyValueDatabase, service, utils, Result};
 
 impl service::rooms::auth_chain::Data for KeyValueDatabase {
-	fn get_cached_eventid_authchain(&self, key: &[u64]) -> Result<Option<Arc<HashSet<u64>>>> {
+	fn get_cached_eventid_authchain(&self, key: &[u64]) -> Result<Option<Arc<[u64]>>> {
 		// Check RAM cache
 		if let Some(result) = self.auth_chain_cache.lock().unwrap().get_mut(key) {
 			return Ok(Some(Arc::clone(result)));
@@ -19,12 +19,10 @@ impl service::rooms::auth_chain::Data for KeyValueDatabase {
 					chain
 						.chunks_exact(size_of::<u64>())
 						.map(|chunk| utils::u64_from_bytes(chunk).expect("byte length is correct"))
-						.collect()
+						.collect::<Arc<[u64]>>()
 				});
 
 			if let Some(chain) = chain {
-				let chain = Arc::new(chain);
-
 				// Cache in RAM
 				self.auth_chain_cache
 					.lock()
@@ -38,7 +36,7 @@ impl service::rooms::auth_chain::Data for KeyValueDatabase {
 		Ok(None)
 	}
 
-	fn cache_auth_chain(&self, key: Vec<u64>, auth_chain: Arc<HashSet<u64>>) -> Result<()> {
+	fn cache_auth_chain(&self, key: Vec<u64>, auth_chain: Arc<[u64]>) -> Result<()> {
 		// Only persist single events in db
 		if key.len() == 1 {
 			self.shorteventid_authchain.insert(
diff --git a/src/database/mod.rs b/src/database/mod.rs
index 32b99a17..f4eef27a 100644
--- a/src/database/mod.rs
+++ b/src/database/mod.rs
@@ -181,7 +181,7 @@ pub struct KeyValueDatabase {
 	//pub pusher: pusher::PushData,
 	pub(super) senderkey_pusher: Arc<dyn KvTree>,
 
-	pub(super) auth_chain_cache: Mutex<LruCache<Vec<u64>, Arc<HashSet<u64>>>>,
+	pub(super) auth_chain_cache: Mutex<LruCache<Vec<u64>, Arc<[u64]>>>,
 	pub(super) our_real_users_cache: RwLock<HashMap<OwnedRoomId, Arc<HashSet<OwnedUserId>>>>,
 	pub(super) appservice_in_room_cache: RwLock<HashMap<OwnedRoomId, HashMap<String, bool>>>,
 	pub(super) lasttimelinecount_cache: Mutex<HashMap<OwnedRoomId, PduCount>>,
diff --git a/src/service/rooms/auth_chain/data.rs b/src/service/rooms/auth_chain/data.rs
index c83b4eb0..f77d2d90 100644
--- a/src/service/rooms/auth_chain/data.rs
+++ b/src/service/rooms/auth_chain/data.rs
@@ -1,8 +1,8 @@
-use std::{collections::HashSet, sync::Arc};
+use std::sync::Arc;
 
 use crate::Result;
 
 pub trait Data: Send + Sync {
-	fn get_cached_eventid_authchain(&self, shorteventid: &[u64]) -> Result<Option<Arc<HashSet<u64>>>>;
-	fn cache_auth_chain(&self, shorteventid: Vec<u64>, auth_chain: Arc<HashSet<u64>>) -> Result<()>;
+	fn get_cached_eventid_authchain(&self, shorteventid: &[u64]) -> Result<Option<Arc<[u64]>>>;
+	fn cache_auth_chain(&self, shorteventid: Vec<u64>, auth_chain: Arc<[u64]>) -> Result<()>;
 }
diff --git a/src/service/rooms/auth_chain/mod.rs b/src/service/rooms/auth_chain/mod.rs
index b7f40695..03c49faf 100644
--- a/src/service/rooms/auth_chain/mod.rs
+++ b/src/service/rooms/auth_chain/mod.rs
@@ -15,15 +15,6 @@ pub struct Service {
 }
 
 impl Service {
-	pub fn get_cached_eventid_authchain(&self, key: &[u64]) -> Result<Option<Arc<HashSet<u64>>>> {
-		self.db.get_cached_eventid_authchain(key)
-	}
-
-	#[tracing::instrument(skip(self))]
-	pub fn cache_auth_chain(&self, key: Vec<u64>, auth_chain: Arc<HashSet<u64>>) -> Result<()> {
-		self.db.cache_auth_chain(key, auth_chain)
-	}
-
 	pub async fn get_auth_chain<'a>(
 		&self, room_id: &RoomId, starting_events: Vec<Arc<EventId>>,
 	) -> Result<impl Iterator<Item = Arc<EventId>> + 'a> {
@@ -81,7 +72,7 @@ impl Service {
 					services()
 						.rooms
 						.auth_chain
-						.cache_auth_chain(vec![sevent_id], Arc::clone(&auth_chain))?;
+						.cache_auth_chain(vec![sevent_id], &auth_chain)?;
 					debug!(
 						event_id = ?event_id,
 						chain_length = ?auth_chain.len(),
@@ -105,7 +96,7 @@ impl Service {
 			services()
 				.rooms
 				.auth_chain
-				.cache_auth_chain(chunk_key, Arc::clone(&chunk_cache))?;
+				.cache_auth_chain(chunk_key, &chunk_cache)?;
 			full_auth_chain.extend(chunk_cache.iter());
 		}
 
@@ -154,4 +145,14 @@ impl Service {
 
 		Ok(found)
 	}
+
+	pub fn get_cached_eventid_authchain(&self, key: &[u64]) -> Result<Option<Arc<[u64]>>> {
+		self.db.get_cached_eventid_authchain(key)
+	}
+
+	#[tracing::instrument(skip(self))]
+	pub fn cache_auth_chain(&self, key: Vec<u64>, auth_chain: &HashSet<u64>) -> Result<()> {
+		self.db
+			.cache_auth_chain(key, auth_chain.iter().copied().collect::<Arc<[u64]>>())
+	}
 }