diff --git a/Cargo.toml b/Cargo.toml
index c93c6736..19ccbb00 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -769,7 +769,7 @@ perf = "warn"
 ###################
 #restriction = "warn"
 
-#arithmetic_side_effects = "warn"                                    # TODO
+arithmetic_side_effects = "warn"
 #as_conversions = "warn"                                             # TODO
 assertions_on_result_states = "warn"
 dbg_macro = "warn"
diff --git a/src/admin/debug/commands.rs b/src/admin/debug/commands.rs
index 3efe283b..53009566 100644
--- a/src/admin/debug/commands.rs
+++ b/src/admin/debug/commands.rs
@@ -58,7 +58,7 @@ pub(super) async fn parse_pdu(body: Vec<&str>) -> Result<RoomMessageEventContent
 		));
 	}
 
-	let string = body[1..body.len() - 1].join("\n");
+	let string = body[1..body.len().saturating_sub(1)].join("\n");
 	match serde_json::from_str(&string) {
 		Ok(value) => match ruma::signatures::reference_hash(&value, &RoomVersionId::V6) {
 			Ok(hash) => {
diff --git a/src/admin/room/room_moderation_commands.rs b/src/admin/room/room_moderation_commands.rs
index 39eb7c47..92e3de47 100644
--- a/src/admin/room/room_moderation_commands.rs
+++ b/src/admin/room/room_moderation_commands.rs
@@ -191,7 +191,10 @@ async fn ban_list_of_rooms(body: Vec<&str>, force: bool, disable_federation: boo
 		));
 	}
 
-	let rooms_s = body.clone().drain(1..body.len() - 1).collect::<Vec<_>>();
+	let rooms_s = body
+		.clone()
+		.drain(1..body.len().saturating_sub(1))
+		.collect::<Vec<_>>();
 
 	let admin_room_alias = &services().globals.admin_alias;
 
diff --git a/src/admin/user/commands.rs b/src/admin/user/commands.rs
index 6dc60713..884e1d29 100644
--- a/src/admin/user/commands.rs
+++ b/src/admin/user/commands.rs
@@ -23,7 +23,7 @@ pub(super) async fn list(_body: Vec<&str>) -> Result<RoomMessageEventContent> {
 	match services().users.list_local_users() {
 		Ok(users) => {
 			let mut plain_msg = format!("Found {} local user account(s):\n```\n", users.len());
-			plain_msg += &users.join("\n");
+			plain_msg += users.join("\n").as_str();
 			plain_msg += "\n```";
 
 			Ok(RoomMessageEventContent::notice_markdown(plain_msg))
@@ -195,7 +195,10 @@ pub(super) async fn deactivate_all(
 		));
 	}
 
-	let usernames = body.clone().drain(1..body.len() - 1).collect::<Vec<_>>();
+	let usernames = body
+		.clone()
+		.drain(1..body.len().saturating_sub(1))
+		.collect::<Vec<_>>();
 
 	let mut user_ids: Vec<OwnedUserId> = Vec::with_capacity(usernames.len());
 	let mut admins = Vec::new();
diff --git a/src/core/utils/html.rs b/src/core/utils/html.rs
index 3b44a31b..938e50ec 100644
--- a/src/core/utils/html.rs
+++ b/src/core/utils/html.rs
@@ -26,7 +26,7 @@ impl fmt::Display for Escape<'_> {
 			fmt.write_str(s)?;
 			// NOTE: we only expect single byte characters here - which is fine as long as
 			// we only match single byte characters
-			last = i + 1;
+			last = i.saturating_add(1);
 		}
 
 		if last < s.len() {
diff --git a/src/core/utils/math.rs b/src/core/utils/math.rs
index a77f8e26..f00b9055 100644
--- a/src/core/utils/math.rs
+++ b/src/core/utils/math.rs
@@ -16,7 +16,15 @@ macro_rules! checked {
 #[cfg(not(debug_assertions))]
 #[macro_export]
 macro_rules! validated {
-	($($input:tt)*) => { Ok($($input)*) }
+	($($input:tt)*) => {
+		//#[allow(clippy::arithmetic_side_effects)] {
+		//Some($($input)*)
+		//	.ok_or_else(|| $crate::Error::Arithmetic("this error should never been seen"))
+		//}
+
+		//NOTE: remove me when stmt_expr_attributes is stable
+		$crate::checked!($($input)*)
+	}
 }
 
 #[cfg(debug_assertions)]
diff --git a/src/core/utils/rand.rs b/src/core/utils/rand.rs
index 1ded8a6d..b80671eb 100644
--- a/src/core/utils/rand.rs
+++ b/src/core/utils/rand.rs
@@ -15,7 +15,11 @@ pub fn string(length: usize) -> String {
 
 #[inline]
 #[must_use]
-pub fn timepoint_secs(range: Range<u64>) -> SystemTime { SystemTime::now() + secs(range) }
+pub fn timepoint_secs(range: Range<u64>) -> SystemTime {
+	SystemTime::now()
+		.checked_add(secs(range))
+		.expect("range does not overflow SystemTime")
+}
 
 #[must_use]
 pub fn secs(range: Range<u64>) -> Duration {
diff --git a/src/core/utils/tests.rs b/src/core/utils/tests.rs
index 239e27e9..add15861 100644
--- a/src/core/utils/tests.rs
+++ b/src/core/utils/tests.rs
@@ -65,7 +65,7 @@ fn common_prefix_none() {
 
 #[test]
 fn checked_add() {
-	use utils::math::checked;
+	use crate::checked;
 
 	let a = 1234;
 	let res = checked!(a + 1).unwrap();
@@ -75,9 +75,9 @@ fn checked_add() {
 #[test]
 #[should_panic(expected = "overflow")]
 fn checked_add_overflow() {
-	use utils::math::checked;
+	use crate::checked;
 
-	let a: u64 = u64::MAX;
+	let a = u64::MAX;
 	let res = checked!(a + 1).expect("overflow");
 	assert_eq!(res, 0);
 }
diff --git a/src/service/globals/data.rs b/src/service/globals/data.rs
index ecb827fe..083aec3c 100644
--- a/src/service/globals/data.rs
+++ b/src/service/globals/data.rs
@@ -65,7 +65,10 @@ impl Data {
 			"counter mismatch"
 		);
 
-		*counter = counter.wrapping_add(1);
+		*counter = counter
+			.checked_add(1)
+			.expect("counter must not overflow u64");
+
 		self.global.insert(COUNTER, &counter.to_be_bytes())?;
 
 		Ok(*counter)
diff --git a/src/service/globals/migrations.rs b/src/service/globals/migrations.rs
index e171cb9d..3948d1f5 100644
--- a/src/service/globals/migrations.rs
+++ b/src/service/globals/migrations.rs
@@ -836,11 +836,14 @@ async fn fix_bad_double_separator_in_state_cache(db: &Arc<Database>, _config: &C
 	for (mut key, value) in roomuserid_joined.iter() {
 		iter_count = iter_count.saturating_add(1);
 		debug_info!(%iter_count);
-		let first_sep_index = key.iter().position(|&i| i == 0xFF).unwrap();
+		let first_sep_index = key
+			.iter()
+			.position(|&i| i == 0xFF)
+			.expect("found 0xFF delim");
 
 		if key
 			.iter()
-			.get(first_sep_index..=first_sep_index + 1)
+			.get(first_sep_index..=first_sep_index.saturating_add(1))
 			.copied()
 			.collect_vec()
 			== vec![0xFF, 0xFF]
diff --git a/src/service/media/mod.rs b/src/service/media/mod.rs
index caa75d4e..3cb8fda8 100644
--- a/src/service/media/mod.rs
+++ b/src/service/media/mod.rs
@@ -1,10 +1,10 @@
 mod data;
 mod tests;
 
-use std::{collections::HashMap, io::Cursor, path::PathBuf, sync::Arc, time::SystemTime};
+use std::{collections::HashMap, io::Cursor, num::Saturating as Sat, path::PathBuf, sync::Arc, time::SystemTime};
 
 use base64::{engine::general_purpose, Engine as _};
-use conduit::{debug, debug_error, error, utils, Error, Result, Server};
+use conduit::{checked, debug, debug_error, error, utils, Error, Result, Server};
 use data::Data;
 use image::imageops::FilterType;
 use ruma::{OwnedMxcUri, OwnedUserId};
@@ -305,36 +305,20 @@ impl Service {
 					image.resize_to_fill(width, height, FilterType::CatmullRom)
 				} else {
 					let (exact_width, exact_height) = {
-						// Copied from image::dynimage::resize_dimensions
-						//
-						// https://github.com/image-rs/image/blob/6edf8ae492c4bb1dacb41da88681ea74dab1bab3/src/math/utils.rs#L5-L11
-						// Calculates the width and height an image should be
-						// resized to. This preserves aspect ratio, and based
-						// on the `fill` parameter will either fill the
-						// dimensions to fit inside the smaller constraint
-						// (will overflow the specified bounds on one axis to
-						// preserve aspect ratio), or will shrink so that both
-						// dimensions are completely contained within the given
-						// `width` and `height`, with empty space on one axis.
-						let ratio = u64::from(original_width) * u64::from(height);
-						let nratio = u64::from(width) * u64::from(original_height);
+						let ratio = Sat(original_width) * Sat(height);
+						let nratio = Sat(width) * Sat(original_height);
 
 						let use_width = nratio <= ratio;
 						let intermediate = if use_width {
-							u64::from(original_height) * u64::from(width) / u64::from(original_width)
+							Sat(original_height) * Sat(checked!(width / original_width)?)
 						} else {
-							u64::from(original_width) * u64::from(height) / u64::from(original_height)
+							Sat(original_width) * Sat(checked!(height / original_height)?)
 						};
+
 						if use_width {
-							if u32::try_from(intermediate).is_ok() {
-								(width, intermediate as u32)
-							} else {
-								((u64::from(width) * u64::from(u32::MAX) / intermediate) as u32, u32::MAX)
-							}
-						} else if u32::try_from(intermediate).is_ok() {
-							(intermediate as u32, height)
+							(width, intermediate.0)
 						} else {
-							(u32::MAX, (u64::from(height) * u64::from(u32::MAX) / intermediate) as u32)
+							(intermediate.0, height)
 						}
 					};
 
diff --git a/src/service/presence/mod.rs b/src/service/presence/mod.rs
index 584f1a6d..f5400379 100644
--- a/src/service/presence/mod.rs
+++ b/src/service/presence/mod.rs
@@ -3,7 +3,7 @@ mod data;
 use std::{sync::Arc, time::Duration};
 
 use async_trait::async_trait;
-use conduit::{debug, error, utils, Error, Result};
+use conduit::{checked, debug, error, utils, Error, Result};
 use data::Data;
 use futures_util::{stream::FuturesUnordered, StreamExt};
 use ruma::{
@@ -79,12 +79,16 @@ pub struct Service {
 	timer_receiver: Mutex<loole::Receiver<(OwnedUserId, Duration)>>,
 	handler_join: Mutex<Option<JoinHandle<()>>>,
 	timeout_remote_users: bool,
+	idle_timeout: u64,
+	offline_timeout: u64,
 }
 
 #[async_trait]
 impl crate::Service for Service {
 	fn build(args: crate::Args<'_>) -> Result<Arc<Self>> {
 		let config = &args.server.config;
+		let idle_timeout_s = config.presence_idle_timeout_s;
+		let offline_timeout_s = config.presence_offline_timeout_s;
 		let (timer_sender, timer_receiver) = loole::unbounded();
 		Ok(Arc::new(Self {
 			db: Data::new(args.db),
@@ -92,6 +96,8 @@ impl crate::Service for Service {
 			timer_receiver: Mutex::new(timer_receiver),
 			handler_join: Mutex::new(None),
 			timeout_remote_users: config.presence_timeout_remote_users,
+			idle_timeout: checked!(idle_timeout_s * 1_000)?,
+			offline_timeout: checked!(offline_timeout_s * 1_000)?,
 		}))
 	}
 
@@ -219,7 +225,7 @@ impl Service {
 		loop {
 			debug_assert!(!receiver.is_closed(), "channel error");
 			tokio::select! {
-				Some(user_id) = presence_timers.next() => process_presence_timer(&user_id)?,
+				Some(user_id) = presence_timers.next() => self.process_presence_timer(&user_id)?,
 				event = receiver.recv_async() => match event {
 					Err(_e) => return Ok(()),
 					Ok((user_id, timeout)) => {
@@ -230,6 +236,36 @@ impl Service {
 			}
 		}
 	}
+
+	fn process_presence_timer(&self, user_id: &OwnedUserId) -> Result<()> {
+		let mut presence_state = PresenceState::Offline;
+		let mut last_active_ago = None;
+		let mut status_msg = None;
+
+		let presence_event = self.get_presence(user_id)?;
+
+		if let Some(presence_event) = presence_event {
+			presence_state = presence_event.content.presence;
+			last_active_ago = presence_event.content.last_active_ago;
+			status_msg = presence_event.content.status_msg;
+		}
+
+		let new_state = match (&presence_state, last_active_ago.map(u64::from)) {
+			(PresenceState::Online, Some(ago)) if ago >= self.idle_timeout => Some(PresenceState::Unavailable),
+			(PresenceState::Unavailable, Some(ago)) if ago >= self.offline_timeout => Some(PresenceState::Offline),
+			_ => None,
+		};
+
+		debug!(
+			"Processed presence timer for user '{user_id}': Old state = {presence_state}, New state = {new_state:?}"
+		);
+
+		if let Some(new_state) = new_state {
+			self.set_presence(user_id, &new_state, Some(false), last_active_ago, status_msg)?;
+		}
+
+		Ok(())
+	}
 }
 
 async fn presence_timer(user_id: OwnedUserId, timeout: Duration) -> OwnedUserId {
@@ -237,36 +273,3 @@ async fn presence_timer(user_id: OwnedUserId, timeout: Duration) -> OwnedUserId
 
 	user_id
 }
-
-fn process_presence_timer(user_id: &OwnedUserId) -> Result<()> {
-	let idle_timeout = services().globals.config.presence_idle_timeout_s * 1_000;
-	let offline_timeout = services().globals.config.presence_offline_timeout_s * 1_000;
-
-	let mut presence_state = PresenceState::Offline;
-	let mut last_active_ago = None;
-	let mut status_msg = None;
-
-	let presence_event = services().presence.get_presence(user_id)?;
-
-	if let Some(presence_event) = presence_event {
-		presence_state = presence_event.content.presence;
-		last_active_ago = presence_event.content.last_active_ago;
-		status_msg = presence_event.content.status_msg;
-	}
-
-	let new_state = match (&presence_state, last_active_ago.map(u64::from)) {
-		(PresenceState::Online, Some(ago)) if ago >= idle_timeout => Some(PresenceState::Unavailable),
-		(PresenceState::Unavailable, Some(ago)) if ago >= offline_timeout => Some(PresenceState::Offline),
-		_ => None,
-	};
-
-	debug!("Processed presence timer for user '{user_id}': Old state = {presence_state}, New state = {new_state:?}");
-
-	if let Some(new_state) = new_state {
-		services()
-			.presence
-			.set_presence(user_id, &new_state, Some(false), last_active_ago, status_msg)?;
-	}
-
-	Ok(())
-}
diff --git a/src/service/rooms/auth_chain/mod.rs b/src/service/rooms/auth_chain/mod.rs
index ca04b1e5..18cdb70f 100644
--- a/src/service/rooms/auth_chain/mod.rs
+++ b/src/service/rooms/auth_chain/mod.rs
@@ -5,7 +5,7 @@ use std::{
 	sync::Arc,
 };
 
-use conduit::{debug, error, trace, warn, Error, Result};
+use conduit::{debug, error, trace, validated, warn, Error, Result};
 use data::Data;
 use ruma::{api::client::error::ErrorKind, EventId, RoomId};
 
@@ -43,20 +43,20 @@ impl Service {
 
 	#[tracing::instrument(skip_all, name = "auth_chain")]
 	pub async fn get_auth_chain(&self, room_id: &RoomId, starting_events: &[&EventId]) -> Result<Vec<u64>> {
-		const NUM_BUCKETS: usize = 50; //TODO: change possible w/o disrupting db?
+		const NUM_BUCKETS: u64 = 50; //TODO: change possible w/o disrupting db?
 		const BUCKET: BTreeSet<(u64, &EventId)> = BTreeSet::new();
 
 		let started = std::time::Instant::now();
-		let mut buckets = [BUCKET; NUM_BUCKETS];
-		for (i, short) in services()
+		let mut buckets = [BUCKET; NUM_BUCKETS as usize];
+		for (i, &short) in services()
 			.rooms
 			.short
 			.multi_get_or_create_shorteventid(starting_events)?
 			.iter()
 			.enumerate()
 		{
-			let bucket = short % NUM_BUCKETS as u64;
-			buckets[bucket as usize].insert((*short, starting_events[i]));
+			let bucket = validated!(short % NUM_BUCKETS)?;
+			buckets[bucket as usize].insert((short, starting_events[i]));
 		}
 
 		debug!(
diff --git a/src/service/rooms/event_handler/mod.rs b/src/service/rooms/event_handler/mod.rs
index 395b70f2..0f7919dd 100644
--- a/src/service/rooms/event_handler/mod.rs
+++ b/src/service/rooms/event_handler/mod.rs
@@ -191,7 +191,7 @@ impl Service {
 							e.insert((Instant::now(), 1));
 						},
 						hash_map::Entry::Occupied(mut e) => {
-							*e.get_mut() = (Instant::now(), e.get().1 + 1);
+							*e.get_mut() = (Instant::now(), e.get().1.saturating_add(1));
 						},
 					};
 				},
@@ -1072,7 +1072,7 @@ impl Service {
 				let mut todo_auth_events = vec![Arc::clone(id)];
 				let mut events_in_reverse_order = Vec::with_capacity(todo_auth_events.len());
 				let mut events_all = HashSet::with_capacity(todo_auth_events.len());
-				let mut i = 0;
+				let mut i: u64 = 0;
 				while let Some(next_id) = todo_auth_events.pop() {
 					if let Some((time, tries)) = services()
 						.globals
@@ -1094,7 +1094,7 @@ impl Service {
 						continue;
 					}
 
-					i += 1;
+					i = i.saturating_add(1);
 					if i % 100 == 0 {
 						tokio::task::yield_now().await;
 					}
diff --git a/src/service/rooms/pdu_metadata/mod.rs b/src/service/rooms/pdu_metadata/mod.rs
index e35c969d..cdb2fc29 100644
--- a/src/service/rooms/pdu_metadata/mod.rs
+++ b/src/service/rooms/pdu_metadata/mod.rs
@@ -205,7 +205,7 @@ impl Service {
 					if let Ok(relations) = self.db.relations_until(user_id, room_id, target, until) {
 						for relation in relations.flatten() {
 							if stack_pdu.1 < max_depth {
-								stack.push((relation.clone(), stack_pdu.1 + 1));
+								stack.push((relation.clone(), stack_pdu.1.saturating_add(1)));
 							}
 
 							pdus.push(relation);
diff --git a/src/service/rooms/read_receipt/data.rs b/src/service/rooms/read_receipt/data.rs
index 17acb0b3..06eaf655 100644
--- a/src/service/rooms/read_receipt/data.rs
+++ b/src/service/rooms/read_receipt/data.rs
@@ -76,10 +76,12 @@ impl Data {
 				.iter_from(&first_possible_edu, false)
 				.take_while(move |(k, _)| k.starts_with(&prefix2))
 				.map(move |(k, v)| {
-					let count = utils::u64_from_bytes(&k[prefix.len()..prefix.len() + size_of::<u64>()])
+					let count_offset = prefix.len().saturating_add(size_of::<u64>());
+					let count = utils::u64_from_bytes(&k[prefix.len()..count_offset])
 						.map_err(|_| Error::bad_database("Invalid readreceiptid count in db."))?;
+					let user_id_offset = count_offset.saturating_add(1);
 					let user_id = UserId::parse(
-						utils::string_from_bytes(&k[prefix.len() + size_of::<u64>() + 1..])
+						utils::string_from_bytes(&k[user_id_offset..])
 							.map_err(|_| Error::bad_database("Invalid readreceiptid userid bytes in db."))?,
 					)
 					.map_err(|_| Error::bad_database("Invalid readreceiptid userid in db."))?;
diff --git a/src/service/rooms/spaces/mod.rs b/src/service/rooms/spaces/mod.rs
index bf6cc873..6924c50e 100644
--- a/src/service/rooms/spaces/mod.rs
+++ b/src/service/rooms/spaces/mod.rs
@@ -7,7 +7,7 @@ use std::{
 	sync::Arc,
 };
 
-use conduit::debug_info;
+use conduit::{checked, debug_info};
 use lru_cache::LruCache;
 use ruma::{
 	api::{
@@ -508,7 +508,8 @@ impl Service {
 							}
 
 							// We have reached the room after where we last left off
-							if parents.len() + 1 == short_room_ids.len() {
+							let parents_len = parents.len();
+							if checked!(parents_len + 1)? == short_room_ids.len() {
 								populate_results = true;
 							}
 						}
diff --git a/src/service/rooms/state_compressor/data.rs b/src/service/rooms/state_compressor/data.rs
index 61c7d6e6..33773001 100644
--- a/src/service/rooms/state_compressor/data.rs
+++ b/src/service/rooms/state_compressor/data.rs
@@ -1,6 +1,6 @@
 use std::{collections::HashSet, mem::size_of, sync::Arc};
 
-use conduit::{utils, Error, Result};
+use conduit::{checked, utils, Error, Result};
 use database::{Database, Map};
 
 use super::CompressedStateEvent;
@@ -38,11 +38,12 @@ impl Data {
 		let mut added = HashSet::new();
 		let mut removed = HashSet::new();
 
-		let mut i = size_of::<u64>();
-		while let Some(v) = value.get(i..i + 2 * size_of::<u64>()) {
+		let stride = size_of::<u64>();
+		let mut i = stride;
+		while let Some(v) = value.get(i..checked!(i + 2 * stride)?) {
 			if add_mode && v.starts_with(&0_u64.to_be_bytes()) {
 				add_mode = false;
-				i += size_of::<u64>();
+				i = checked!(i + stride)?;
 				continue;
 			}
 			if add_mode {
@@ -50,7 +51,7 @@ impl Data {
 			} else {
 				removed.insert(v.try_into().expect("we checked the size above"));
 			}
-			i += 2 * size_of::<u64>();
+			i = checked!(i + 2 * stride)?;
 		}
 
 		Ok(StateDiff {
diff --git a/src/service/rooms/state_compressor/mod.rs b/src/service/rooms/state_compressor/mod.rs
index 97f3fb80..ca076fc9 100644
--- a/src/service/rooms/state_compressor/mod.rs
+++ b/src/service/rooms/state_compressor/mod.rs
@@ -7,7 +7,7 @@ use std::{
 	sync::{Arc, Mutex as StdMutex, Mutex},
 };
 
-use conduit::{utils, Result};
+use conduit::{checked, utils, Result};
 use data::Data;
 use lru_cache::LruCache;
 use ruma::{EventId, RoomId};
@@ -169,12 +169,14 @@ impl Service {
 		statediffremoved: Arc<HashSet<CompressedStateEvent>>, diff_to_sibling: usize,
 		mut parent_states: ParentStatesVec,
 	) -> Result<()> {
-		let diffsum = statediffnew.len() + statediffremoved.len();
+		let statediffnew_len = statediffnew.len();
+		let statediffremoved_len = statediffremoved.len();
+		let diffsum = checked!(statediffnew_len + statediffremoved_len)?;
 
 		if parent_states.len() > 3 {
 			// Number of layers
 			// To many layers, we have to go deeper
-			let parent = parent_states.pop().unwrap();
+			let parent = parent_states.pop().expect("parent must have a state");
 
 			let mut parent_new = (*parent.2).clone();
 			let mut parent_removed = (*parent.3).clone();
@@ -226,10 +228,12 @@ impl Service {
 		// 1. We add the current diff on top of the parent layer.
 		// 2. We replace a layer above
 
-		let parent = parent_states.pop().unwrap();
-		let parent_diff = parent.2.len() + parent.3.len();
+		let parent = parent_states.pop().expect("parent must have a state");
+		let parent_2_len = parent.2.len();
+		let parent_3_len = parent.3.len();
+		let parent_diff = checked!(parent_2_len + parent_3_len)?;
 
-		if diffsum * diffsum >= 2 * diff_to_sibling * parent_diff {
+		if checked!(diffsum * diffsum)? >= checked!(2 * diff_to_sibling * parent_diff)? {
 			// Diff too big, we replace above layer(s)
 			let mut parent_new = (*parent.2).clone();
 			let mut parent_removed = (*parent.3).clone();
diff --git a/src/service/rooms/threads/data.rs b/src/service/rooms/threads/data.rs
index 29539847..c4a1a294 100644
--- a/src/service/rooms/threads/data.rs
+++ b/src/service/rooms/threads/data.rs
@@ -1,6 +1,6 @@
 use std::{mem::size_of, sync::Arc};
 
-use conduit::{utils, Error, Result};
+use conduit::{checked, utils, Error, Result};
 use database::{Database, Map};
 use ruma::{api::client::threads::get_threads::v1::IncludeThreads, OwnedUserId, RoomId, UserId};
 
@@ -31,7 +31,7 @@ impl Data {
 			.to_vec();
 
 		let mut current = prefix.clone();
-		current.extend_from_slice(&(until - 1).to_be_bytes());
+		current.extend_from_slice(&(checked!(until - 1)?).to_be_bytes());
 
 		Ok(Box::new(
 			self.threadid_userids
diff --git a/src/service/rooms/threads/mod.rs b/src/service/rooms/threads/mod.rs
index f3cefe21..dd2686b0 100644
--- a/src/service/rooms/threads/mod.rs
+++ b/src/service/rooms/threads/mod.rs
@@ -64,7 +64,7 @@ impl Service {
 				.and_then(|relations| serde_json::from_value::<BundledThread>(relations.clone().into()).ok())
 			{
 				// Thread already existed
-				relations.count += uint!(1);
+				relations.count = relations.count.saturating_add(uint!(1));
 				relations.latest_event = pdu.to_message_like_event();
 
 				let content = serde_json::to_value(relations).expect("to_value always works");
diff --git a/src/service/rooms/timeline/data.rs b/src/service/rooms/timeline/data.rs
index 0d4d945e..ec975b99 100644
--- a/src/service/rooms/timeline/data.rs
+++ b/src/service/rooms/timeline/data.rs
@@ -4,7 +4,7 @@ use std::{
 	sync::{Arc, Mutex},
 };
 
-use conduit::{error, utils, Error, Result};
+use conduit::{checked, error, utils, Error, Result};
 use database::{Database, Map};
 use ruma::{api::client::error::ErrorKind, CanonicalJsonObject, EventId, OwnedRoomId, OwnedUserId, RoomId, UserId};
 
@@ -281,10 +281,12 @@ impl Data {
 
 /// Returns the `count` of this pdu's id.
 pub(super) fn pdu_count(pdu_id: &[u8]) -> Result<PduCount> {
-	let last_u64 = utils::u64_from_bytes(&pdu_id[pdu_id.len() - size_of::<u64>()..])
+	let stride = size_of::<u64>();
+	let pdu_id_len = pdu_id.len();
+	let last_u64 = utils::u64_from_bytes(&pdu_id[checked!(pdu_id_len - stride)?..])
 		.map_err(|_| Error::bad_database("PDU has invalid count bytes."))?;
 	let second_last_u64 =
-		utils::u64_from_bytes(&pdu_id[pdu_id.len() - 2 * size_of::<u64>()..pdu_id.len() - size_of::<u64>()]);
+		utils::u64_from_bytes(&pdu_id[checked!(pdu_id_len - 2 * stride)?..checked!(pdu_id_len - stride)?]);
 
 	if matches!(second_last_u64, Ok(0)) {
 		Ok(PduCount::Backfilled(u64::MAX.saturating_sub(last_u64)))
diff --git a/src/service/rooms/timeline/mod.rs b/src/service/rooms/timeline/mod.rs
index ba987dbd..70f4423c 100644
--- a/src/service/rooms/timeline/mod.rs
+++ b/src/service/rooms/timeline/mod.rs
@@ -6,7 +6,7 @@ use std::{
 	sync::Arc,
 };
 
-use conduit::{debug, error, info, utils, utils::mutex_map, warn, Error, Result};
+use conduit::{debug, error, info, utils, utils::mutex_map, validated, warn, Error, Result};
 use data::Data;
 use itertools::Itertools;
 use rand::prelude::SliceRandom;
@@ -670,7 +670,7 @@ impl Service {
 			.filter_map(|event_id| Some(self.get_pdu(event_id).ok()??.depth))
 			.max()
 			.unwrap_or_else(|| uint!(0))
-			+ uint!(1);
+			.saturating_add(uint!(1));
 
 		let mut unsigned = unsigned.unwrap_or_default();
 
@@ -1240,10 +1240,11 @@ impl Service {
 
 		let insert_lock = services().globals.roomid_mutex_insert.lock(&room_id).await;
 
+		let max = u64::MAX;
 		let count = services().globals.next_count()?;
 		let mut pdu_id = shortroomid.to_be_bytes().to_vec();
 		pdu_id.extend_from_slice(&0_u64.to_be_bytes());
-		pdu_id.extend_from_slice(&(u64::MAX - count).to_be_bytes());
+		pdu_id.extend_from_slice(&(validated!(max - count)?).to_be_bytes());
 
 		// Insert pdu
 		self.db.prepend_backfill_pdu(&pdu_id, &event_id, &value)?;
diff --git a/src/service/sending/sender.rs b/src/service/sending/sender.rs
index 0f4fa17a..0fb0d9dc 100644
--- a/src/service/sending/sender.rs
+++ b/src/service/sending/sender.rs
@@ -93,7 +93,7 @@ impl Service {
 		statuses.entry(dest).and_modify(|e| {
 			*e = match e {
 				TransactionStatus::Running => TransactionStatus::Failed(1, Instant::now()),
-				TransactionStatus::Retrying(n) => TransactionStatus::Failed(*n + 1, Instant::now()),
+				TransactionStatus::Retrying(ref n) => TransactionStatus::Failed(n.saturating_add(1), Instant::now()),
 				TransactionStatus::Failed(..) => panic!("Request that was not even running failed?!"),
 			}
 		});
diff --git a/src/service/users/data.rs b/src/service/users/data.rs
index 3ba54a93..302eae9d 100644
--- a/src/service/users/data.rs
+++ b/src/service/users/data.rs
@@ -463,7 +463,8 @@ impl Data {
 					.algorithm(),
 				)
 			}) {
-			*counts.entry(algorithm?).or_default() += uint!(1);
+			let count: &mut UInt = counts.entry(algorithm?).or_default();
+			*count = count.saturating_add(uint!(1));
 		}
 
 		Ok(counts)
@@ -814,7 +815,7 @@ impl Data {
 			.map(|(key, _)| {
 				Ok::<_, Error>((
 					key.clone(),
-					utils::u64_from_bytes(&key[key.len() - size_of::<u64>()..key.len()])
+					utils::u64_from_bytes(&key[key.len().saturating_sub(size_of::<u64>())..key.len()])
 						.map_err(|_| Error::bad_database("ToDeviceId has invalid count bytes."))?,
 				))
 			})
@@ -928,10 +929,12 @@ impl Data {
 	/// Creates an OpenID token, which can be used to prove that a user has
 	/// access to an account (primarily for integrations)
 	pub(super) fn create_openid_token(&self, user_id: &UserId, token: &str) -> Result<u64> {
-		let expires_in = services().globals.config.openid_token_ttl;
-		let expires_at = utils::millis_since_unix_epoch().saturating_add(expires_in * 1000);
+		use std::num::Saturating as Sat;
 
-		let mut value = expires_at.to_be_bytes().to_vec();
+		let expires_in = services().globals.config.openid_token_ttl;
+		let expires_at = Sat(utils::millis_since_unix_epoch()) + Sat(expires_in) * Sat(1000);
+
+		let mut value = expires_at.0.to_be_bytes().to_vec();
 		value.extend_from_slice(user_id.as_bytes());
 
 		self.openidtoken_expiresatuserid