diff --git a/src/service/rooms/auth_chain/mod.rs b/src/service/rooms/auth_chain/mod.rs
index 796eb5d2..67883d01 100644
--- a/src/service/rooms/auth_chain/mod.rs
+++ b/src/service/rooms/auth_chain/mod.rs
@@ -1,7 +1,7 @@
 mod data;
 
 use std::{
-	collections::{BTreeSet, HashSet},
+	collections::{BTreeSet, HashSet, VecDeque},
 	fmt::Debug,
 	sync::Arc,
 };
@@ -185,10 +185,10 @@ impl Service {
 		room_id: &RoomId,
 		event_id: &EventId,
 	) -> Result<HashSet<ShortEventId>> {
-		let mut todo = vec![event_id.to_owned()];
+		let mut todo: VecDeque<_> = [event_id.to_owned()].into();
 		let mut found = HashSet::new();
 
-		while let Some(event_id) = todo.pop() {
+		while let Some(event_id) = todo.pop_front() {
 			trace!(?event_id, "processing auth event");
 
 			match self.services.timeline.get_pdu(&event_id).await {
@@ -218,7 +218,8 @@ impl Service {
 								?auth_event,
 								"adding auth event to processing queue"
 							);
-							todo.push(auth_event.clone());
+
+							todo.push_back(auth_event.clone());
 						}
 					}
 				},
diff --git a/src/service/rooms/event_handler/fetch_and_handle_outliers.rs b/src/service/rooms/event_handler/fetch_and_handle_outliers.rs
index f980ca24..1bad4659 100644
--- a/src/service/rooms/event_handler/fetch_and_handle_outliers.rs
+++ b/src/service/rooms/event_handler/fetch_and_handle_outliers.rs
@@ -1,5 +1,5 @@
 use std::{
-	collections::{hash_map, BTreeMap, HashSet},
+	collections::{hash_map, BTreeMap, HashSet, VecDeque},
 	sync::Arc,
 	time::Instant,
 };
@@ -62,10 +62,10 @@ pub(super) async fn fetch_and_handle_outliers<'a>(
 		// c. Ask origin server over federation
 		// We also handle its auth chain here so we don't get a stack overflow in
 		// handle_outlier_pdu.
-		let mut todo_auth_events = vec![id.clone()];
+		let mut todo_auth_events: VecDeque<_> = [id.clone()].into();
 		let mut events_in_reverse_order = Vec::with_capacity(todo_auth_events.len());
 		let mut events_all = HashSet::with_capacity(todo_auth_events.len());
-		while let Some(next_id) = todo_auth_events.pop() {
+		while let Some(next_id) = todo_auth_events.pop_front() {
 			if let Some((time, tries)) = self
 				.services
 				.globals
@@ -132,7 +132,7 @@ pub(super) async fn fetch_and_handle_outliers<'a>(
 							if let Ok(auth_event) =
 								serde_json::from_value::<OwnedEventId>(auth_event.clone().into())
 							{
-								todo_auth_events.push(auth_event);
+								todo_auth_events.push_back(auth_event);
 							} else {
 								warn!("Auth event id is not valid");
 							}
diff --git a/src/service/rooms/event_handler/fetch_prev.rs b/src/service/rooms/event_handler/fetch_prev.rs
index ca93e11d..3f121f69 100644
--- a/src/service/rooms/event_handler/fetch_prev.rs
+++ b/src/service/rooms/event_handler/fetch_prev.rs
@@ -1,5 +1,5 @@
 use std::{
-	collections::{BTreeMap, HashMap, HashSet},
+	collections::{BTreeMap, HashMap, HashSet, VecDeque},
 	sync::Arc,
 };
 
@@ -30,13 +30,13 @@ pub(super) async fn fetch_prev(
 )> {
 	let mut graph: HashMap<OwnedEventId, _> = HashMap::with_capacity(initial_set.len());
 	let mut eventid_info = HashMap::new();
-	let mut todo_outlier_stack: Vec<OwnedEventId> = initial_set;
+	let mut todo_outlier_stack: VecDeque<OwnedEventId> = initial_set.into();
 
 	let first_pdu_in_room = self.services.timeline.first_pdu_in_room(room_id).await?;
 
 	let mut amount = 0;
 
-	while let Some(prev_event_id) = todo_outlier_stack.pop() {
+	while let Some(prev_event_id) = todo_outlier_stack.pop_front() {
 		self.services.server.check_running()?;
 
 		if let Some((pdu, mut json_opt)) = self
@@ -74,7 +74,7 @@ pub(super) async fn fetch_prev(
 					amount = amount.saturating_add(1);
 					for prev_prev in &pdu.prev_events {
 						if !graph.contains_key(prev_prev) {
-							todo_outlier_stack.push(prev_prev.clone());
+							todo_outlier_stack.push_back(prev_prev.clone());
 						}
 					}