diff --git a/src/service/rooms/timeline/stitcher/algorithm.rs b/src/service/rooms/timeline/stitcher/algorithm.rs
index 13f0a9be..679859ee 100644
--- a/src/service/rooms/timeline/stitcher/algorithm.rs
+++ b/src/service/rooms/timeline/stitcher/algorithm.rs
@@ -1,7 +1,4 @@
-use std::{
-	cmp::Ordering,
-	collections::{BTreeSet, HashMap, HashSet},
-};
+use std::collections::HashSet;
 
 use indexmap::IndexSet;
 use itertools::Itertools;
@@ -39,7 +36,7 @@ pub(super) struct Stitcher<'backend, B: StitcherBackend> {
 impl<B: StitcherBackend> Stitcher<'_, B> {
 	pub(super) fn new(backend: &B) -> Stitcher<'_, B> { Stitcher { backend } }
 
-	pub(super) fn stitch<'id>(&self, batch: Batch<'id>) -> OrderUpdates<'id, B::Key> {
+	pub(super) fn stitch<'id>(&self, batch: &Batch<'id>) -> OrderUpdates<'id, B::Key> {
 		let mut gap_updates = Vec::new();
 		let mut all_new_events: HashSet<&'id str> = HashSet::new();
 
@@ -100,9 +97,12 @@ impl<B: StitcherBackend> Stitcher<'_, B> {
 			.sorted_by(batch.compare_by_dag_received())
 			.collect_vec();
 
-		let mut items = Vec::with_capacity(
-			events_to_insert.capacity() + events_to_insert.capacity().div_euclid(2),
-		);
+		// allocate 1.5x the size of the to-insert list
+		let items_capacity = events_to_insert
+			.capacity()
+			.saturating_add(events_to_insert.capacity().div_euclid(2));
+
+		let mut items = Vec::with_capacity(items_capacity);
 
 		for event in events_to_insert {
 			let missing_prev_events: HashSet<String> = batch
diff --git a/src/service/rooms/timeline/stitcher/mod.rs b/src/service/rooms/timeline/stitcher/mod.rs
index 471d1357..e3d9e521 100644
--- a/src/service/rooms/timeline/stitcher/mod.rs
+++ b/src/service/rooms/timeline/stitcher/mod.rs
@@ -1,7 +1,4 @@
-use std::{
-	cmp::Ordering,
-	collections::{BTreeMap, HashSet},
-};
+use std::{cmp::Ordering, collections::HashSet};
 
 use indexmap::IndexMap;
 
@@ -58,10 +55,10 @@ pub(super) struct Batch<'id> {
 }
 
 impl<'id> Batch<'id> {
-	pub(super) fn from_edges(edges: EventEdges<'_>) -> Batch<'_> {
+	pub(super) fn from_edges<'edges>(edges: &EventEdges<'edges>) -> Batch<'edges> {
 		let mut events = IndexMap::new();
 
-		for (event, prev_events) in &edges {
+		for (event, prev_events) in edges {
 			let predecessor_set = Self::find_predecessor_set(event, &edges);
 
 			events.insert(*event, EventPredecessors {
diff --git a/src/service/rooms/timeline/stitcher/test/mod.rs b/src/service/rooms/timeline/stitcher/test/mod.rs
index e40b37ed..4a89ab62 100644
--- a/src/service/rooms/timeline/stitcher/test/mod.rs
+++ b/src/service/rooms/timeline/stitcher/test/mod.rs
@@ -36,7 +36,9 @@ impl<'id> TestStitcherBackend<'id> {
 					},
 					| None => unreachable!("we just checked that this index is valid"),
 				}
-				gap_index + 1
+				gap_index.checked_add(1).expect(
+					"should never allocate usize::MAX ids. what kind of test are you running",
+				)
 			};
 
 			let to_insert: Vec<_> = update
@@ -97,8 +99,8 @@ fn run_testcase(testcase: parser::TestCase<'_>) {
 
 	for (index, phase) in testcase.into_iter().enumerate() {
 		let stitcher = Stitcher::new(&backend);
-		let batch = Batch::from_edges(phase.batch);
-		let updates = stitcher.stitch(batch);
+		let batch = Batch::from_edges(&phase.batch);
+		let updates = stitcher.stitch(&batch);
 
 		println!();
 		println!("===== phase {index}");
diff --git a/src/service/rooms/timeline/stitcher/test/parser.rs b/src/service/rooms/timeline/stitcher/test/parser.rs
index 961e0273..9a106430 100644
--- a/src/service/rooms/timeline/stitcher/test/parser.rs
+++ b/src/service/rooms/timeline/stitcher/test/parser.rs
@@ -1,8 +1,8 @@
-use std::collections::{BTreeMap, HashSet};
+use std::collections::HashSet;
 
 use indexmap::IndexMap;
 
-use crate::rooms::timeline::stitcher::{StitchedItem, test};
+use crate::rooms::timeline::stitcher::StitchedItem;
 
 pub(super) type TestEventId<'id> = &'id str;