diff --git a/Cargo.toml b/Cargo.toml
index f52711e..1844d86 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,23 +1,22 @@
 [package]
 name = "rhododendron"
-version = "0.5.0"
+version = "0.6.0"
 authors = ["Parity Technologies <admin@parity.io>"]
 description = "Asynchronously safe BFT protocol, futures-based implementation"
 license = "GPL-3.0"
 repository = "https://github.com/paritytech/rhododendron"
+edition = "2018"
 
 [dependencies]
 futures = "0.1.17"
 error-chain = "0.12"
 log = "0.4"
-parity-codec = { version = "3.0", optional = true }
-parity-codec-derive = { version = "3.0", optional = true }
+parity-codec = { version = "4.1", optional = true, features = ["derive"] }
 
 [dev-dependencies]
 tokio-core = "0.1.12"
 tokio-timer = "0.1.2"
-parity-codec = "3.0"
-parity-codec-derive = "3.0"
+parity-codec = { version = "4.1", features = ["derive"] }
 
 [features]
-codec = ['parity-codec', 'parity-codec-derive']
+codec = ['parity-codec']
diff --git a/src/accumulator.rs b/src/accumulator.rs
index 2136824..bcad3d6 100644
--- a/src/accumulator.rs
+++ b/src/accumulator.rs
@@ -20,7 +20,11 @@ use std::collections::{HashMap, HashSet};
 use std::collections::hash_map::Entry;
 use std::hash::Hash;
 
-use ::{Vote, LocalizedMessage, LocalizedProposal};
+use log::{debug, trace};
+#[cfg(any(test, feature="codec"))]
+use parity_codec::{Encode, Decode};
+
+use crate::{Vote, LocalizedMessage, LocalizedProposal};
 
 /// Justification for some state at a given round.
 #[derive(Debug, Clone, PartialEq, Eq)]
@@ -122,8 +126,8 @@ pub enum State<Candidate, Digest, Signature> {
 #[derive(Debug, Default)]
 #[cfg_attr(any(test, feature="codec"), derive(Encode, Decode))]
 struct VoteCounts {
-	prepared: usize,
-	committed: usize,
+	prepared: u64,
+	committed: u64,
 }
 
 #[derive(Debug)]
@@ -334,7 +338,7 @@ impl<Candidate, Digest, AuthorityId, Signature> Accumulator<Candidate, Digest, A
 				let count = self.vote_counts.entry(digest.clone()).or_insert_with(Default::default);
 				count.prepared += 1;
 
-				if count.prepared >= self.threshold {
+				if count.prepared >= self.threshold as u64 {
 					Some(digest)
 				} else {
 					None
@@ -391,7 +395,7 @@ impl<Candidate, Digest, AuthorityId, Signature> Accumulator<Candidate, Digest, A
 				let count = self.vote_counts.entry(digest.clone()).or_insert_with(Default::default);
 				count.committed += 1;
 
-				if count.committed >= self.threshold {
+				if count.committed >= self.threshold as u64 {
 					Some(digest)
 				} else {
 					None
@@ -458,19 +462,19 @@ impl<Candidate, Digest, AuthorityId, Signature> Accumulator<Candidate, Digest, A
 #[cfg(test)]
 mod tests {
 	use super::*;
-	use ::{LocalizedMessage, LocalizedProposal, LocalizedVote};
+	use crate::{LocalizedMessage, LocalizedProposal, LocalizedVote};
 
 	#[derive(Clone, PartialEq, Eq, Debug, Encode, Decode)]
-	pub struct Candidate(usize);
+	pub struct Candidate(u64);
 
 	#[derive(Hash, PartialEq, Eq, Clone, Debug, Encode, Decode)]
-	pub struct Digest(usize);
+	pub struct Digest(u64);
 
 	#[derive(Hash, PartialEq, Eq, Debug, Encode, Decode, Clone)]
-	pub struct AuthorityId(usize);
+	pub struct AuthorityId(u64);
 
 	#[derive(PartialEq, Eq, Clone, Debug, Encode, Decode)]
-	pub struct Signature(usize, usize);
+	pub struct Signature(u64, u64);
 
 	#[test]
 	fn justification_checks_out() {
diff --git a/src/lib.rs b/src/lib.rs
index f1f5713..27ad9a1 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -35,27 +35,15 @@
 //! Users of the `Agreement` future should schedule it to be pre-empted
 //! by an external import of an agreed value.
 
-#[cfg_attr(test, macro_use)]
-extern crate futures;
-
-#[macro_use]
-extern crate log;
-
-#[cfg(test)]
-extern crate tokio_timer;
-
-#[cfg(any(test, feature="codec"))]
-extern crate parity_codec as codec;
-#[cfg(any(test, feature="codec"))]
-#[macro_use]
-extern crate parity_codec_derive;
-
 use std::collections::{HashMap, BTreeMap, VecDeque};
 use std::collections::hash_map;
 use std::fmt::Debug;
 use std::hash::Hash;
 
 use futures::{future, Future, Stream, Sink, Poll, Async, AsyncSink};
+use log::trace;
+#[cfg(any(test, feature="codec"))]
+use parity_codec::{Encode, Decode};
 
 use self::accumulator::State;
 
@@ -448,7 +436,7 @@ impl<C: Context> Strategy<C> {
 		} else if round_number > current_round {
 			let threshold = bft_threshold(self.nodes, self.max_faulty);
 
-			let mut future_acc = self.future_accumulators.entry(round_number).or_insert_with(|| {
+			let future_acc = self.future_accumulators.entry(round_number).or_insert_with(|| {
 				Accumulator::new(
 					round_number,
 					threshold,
diff --git a/src/tests.rs b/src/tests.rs
index af64ffc..468ec20 100644
--- a/src/tests.rs
+++ b/src/tests.rs
@@ -23,6 +23,7 @@ use std::sync::{Arc, Mutex};
 use std::sync::atomic::{AtomicUsize, Ordering};
 use std::time::Duration;
 
+use futures::try_ready;
 use futures::prelude::*;
 use futures::sync::{oneshot, mpsc};
 use futures::future::FutureResult;
@@ -92,13 +93,13 @@ impl<T: Clone> Future for Network<T> {
 }
 
 #[derive(Debug, PartialEq, Eq, Clone, Encode, Decode, Hash)]
-struct Candidate(usize);
+struct Candidate(u64);
 
 #[derive(Debug, PartialEq, Eq, Clone, Encode, Decode, Hash)]
-struct Digest(usize);
+struct Digest(u64);
 
 #[derive(Debug, PartialEq, Eq, Clone, Encode, Decode, Hash)]
-struct AuthorityId(usize);
+struct AuthorityId(u64);
 
 #[derive(Debug, PartialEq, Eq, Clone, Encode, Decode)]
 struct Signature(Message<Candidate, Digest>, AuthorityId);
@@ -118,7 +119,7 @@ struct TestContext {
 	node_count: usize,
 	current_round: Arc<AtomicUsize>,
 	timer: Timer,
-	evaluated: Mutex<BTreeSet<usize>>,
+	evaluated: Mutex<BTreeSet<u64>>,
 }
 
 impl Context for TestContext {
@@ -140,7 +141,7 @@ impl Context for TestContext {
 			let mut p = self.proposal.lock().unwrap();
 			let x = *p;
 			*p += self.node_count;
-			x
+			x as u64
 		};
 
 		Ok(Candidate(proposal)).into_future()
@@ -173,7 +174,7 @@ impl Context for TestContext {
 	}
 
 	fn round_proposer(&self, round: u32) -> AuthorityId {
-		AuthorityId((round as usize) % self.node_count)
+		AuthorityId((round as u64) % self.node_count as u64)
 	}
 
 	fn proposal_valid(&self, proposal: &Candidate) -> FutureResult<bool, Error> {
@@ -239,7 +240,7 @@ fn consensus_completes_with_minimum_good() {
 		.enumerate()
 		.map(|(i, (tx, rx))| {
 			let ctx = TestContext {
-				local_id: AuthorityId(i),
+				local_id: AuthorityId(i as u64),
 				proposal: Mutex::new(i),
 				current_round: Arc::new(AtomicUsize::new(0)),
 				timer: timer.clone(),
@@ -296,7 +297,7 @@ fn consensus_completes_with_minimum_good_all_initial_proposals_bad() {
 			};
 
 			let ctx = TestContext {
-				local_id: AuthorityId(i),
+				local_id: AuthorityId(i as u64),
 				proposal: Mutex::new(proposal),
 				current_round: Arc::new(AtomicUsize::new(0)),
 				timer: timer.clone(),
@@ -346,7 +347,7 @@ fn consensus_does_not_complete_without_enough_nodes() {
 		.enumerate()
 		.map(|(i, (tx, rx))| {
 			let ctx = TestContext {
-				local_id: AuthorityId(i),
+				local_id: AuthorityId(i as u64),
 				proposal: Mutex::new(i),
 				current_round: Arc::new(AtomicUsize::new(0)),
 				timer: timer.clone(),
@@ -403,7 +404,7 @@ fn threshold_plus_one_locked_on_proposal_only_one_with_candidate() {
 		.enumerate()
 		.map(|(i, (tx, rx))| {
 			let ctx = TestContext {
-				local_id: AuthorityId(i),
+				local_id: AuthorityId(i as u64),
 				proposal: Mutex::new(i),
 				current_round: Arc::new(AtomicUsize::new(locked_round as usize + 1)),
 				timer: timer.clone(),
@@ -483,7 +484,7 @@ fn threshold_plus_one_locked_on_bad_proposal() {
 		.enumerate()
 		.map(|(i, (tx, rx))| {
 			let ctx = TestContext {
-				local_id: AuthorityId(i),
+				local_id: AuthorityId(i as u64),
 				proposal: Mutex::new(i),
 				current_round: Arc::new(AtomicUsize::new(locked_round as usize + 1)),
 				timer: timer.clone(),
@@ -552,7 +553,7 @@ fn consensus_completes_even_when_nodes_start_with_a_delay() {
 		.enumerate()
 		.map(|(i, (tx, rx))| {
 			let ctx = TestContext {
-				local_id: AuthorityId(i),
+				local_id: AuthorityId(i as u64),
 				proposal: Mutex::new(i),
 				current_round: Arc::new(AtomicUsize::new(0)),
 				timer: timer.clone(),