diff --git a/substrate/Cargo.lock b/substrate/Cargo.lock
index fb112d433b..f2296d442e 100644
--- a/substrate/Cargo.lock
+++ b/substrate/Cargo.lock
@@ -1346,10 +1346,11 @@ dependencies = [
 
 [[package]]
 name = "finality-grandpa"
-version = "0.11.2"
+version = "0.12.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "024517816630be5204eba201e8d1d405042b1255a5e0e3f298b054fc24d59e1d"
+checksum = "9d7907cc24468e29b5d3ea2097e78104492b6650c55f96af1f14e7915dc155ad"
 dependencies = [
+ "either",
  "futures 0.3.4",
  "futures-timer 2.0.2",
  "log",
@@ -6344,6 +6345,7 @@ name = "sc-finality-grandpa"
 version = "0.8.0-dev"
 dependencies = [
  "assert_matches",
+ "derive_more",
  "env_logger 0.7.1",
  "finality-grandpa",
  "fork-tree",
diff --git a/substrate/client/finality-grandpa/Cargo.toml b/substrate/client/finality-grandpa/Cargo.toml
index a634595ed3..04c793b58e 100644
--- a/substrate/client/finality-grandpa/Cargo.toml
+++ b/substrate/client/finality-grandpa/Cargo.toml
@@ -14,6 +14,7 @@ targets = ["x86_64-unknown-linux-gnu"]
 
 
 [dependencies]
+derive_more = "0.99.2"
 fork-tree = { version = "2.0.0-dev", path = "../../utils/fork-tree" }
 futures = "0.3.4"
 futures-timer = "3.0.1"
@@ -41,11 +42,11 @@ sp-finality-tracker = { version = "2.0.0-dev", path = "../../primitives/finality
 sp-finality-grandpa = { version = "2.0.0-dev", path = "../../primitives/finality-grandpa" }
 prometheus-endpoint = { package = "substrate-prometheus-endpoint", path = "../../utils/prometheus", version = "0.8.0-dev"}
 sc-block-builder = { version = "0.8.0-dev", path = "../block-builder" }
-finality-grandpa = { version = "0.11.2", features = ["derive-codec"] }
+finality-grandpa = { version = "0.12.0", features = ["derive-codec"] }
 pin-project = "0.4.6"
 
 [dev-dependencies]
-finality-grandpa = { version = "0.11.2", features = ["derive-codec", "test-helpers"] }
+finality-grandpa = { version = "0.12.0", features = ["derive-codec", "test-helpers"] }
 sc-network = { version = "0.8.0-dev", path = "../network" }
 sc-network-test = { version = "0.8.0-dev", path = "../network/test" }
 sp-keyring = { version = "2.0.0-dev", path = "../../primitives/keyring" }
diff --git a/substrate/client/finality-grandpa/src/authorities.rs b/substrate/client/finality-grandpa/src/authorities.rs
index fe3f2dd19e..000c303af7 100644
--- a/substrate/client/finality-grandpa/src/authorities.rs
+++ b/substrate/client/finality-grandpa/src/authorities.rs
@@ -29,6 +29,15 @@ use std::fmt::Debug;
 use std::ops::Add;
 use std::sync::Arc;
 
+/// Error type returned on operations on the `AuthoritySet`.
+#[derive(Debug, derive_more::Display, derive_more::From)]
+pub enum Error<E> {
+	#[display("Invalid authority set, either empty or with an authority weight set to 0.")]
+	InvalidAuthoritySet,
+	#[display(fmt = "Invalid operation in the pending changes tree: {}", _0)]
+	ForkTree(fork_tree::Error<E>),
+}
+
 /// A shared authority set.
 pub(crate) struct SharedAuthoritySet<H, N> {
 	inner: Arc<RwLock<AuthoritySet<H, N>>>,
@@ -64,7 +73,11 @@ where N: Add<Output=N> + Ord + Clone + Debug,
 
 	/// Get the current authorities and their weights (for the current set ID).
 	pub(crate) fn current_authorities(&self) -> VoterSet<AuthorityId> {
-		self.inner.read().current_authorities.iter().cloned().collect()
+		VoterSet::new(self.inner.read().current_authorities.iter().cloned()).expect(
+			"current_authorities is non-empty and weights are non-zero; \
+			 constructor and all mutating operations on `AuthoritySet` ensure this; \
+			 qed.",
+		)
 	}
 }
 
@@ -88,7 +101,7 @@ pub(crate) struct Status<H, N> {
 #[derive(Debug, Clone, Encode, Decode, PartialEq)]
 pub(crate) struct AuthoritySet<H, N> {
 	pub(crate) current_authorities: AuthorityList,
-	pub(crate) set_id: u64,
+	set_id: u64,
 	// Tree of pending standard changes across forks. Standard changes are
 	// enacted on finality and must be enacted (i.e. finalized) in-order across
 	// a given branch
@@ -96,21 +109,49 @@ pub(crate) struct AuthoritySet<H, N> {
 	// Pending forced changes across different forks (at most one per fork).
 	// Forced changes are enacted on block depth (not finality), for this reason
 	// only one forced change should exist per fork.
-	pub(crate) pending_forced_changes: Vec<PendingChange<H, N>>,
+	pending_forced_changes: Vec<PendingChange<H, N>>,
 }
 
 impl<H, N> AuthoritySet<H, N>
 where H: PartialEq,
 	  N: Ord,
 {
+	// authority sets must be non-empty and all weights must be greater than 0
+	fn invalid_authority_list(authorities: &AuthorityList) -> bool {
+		authorities.is_empty() || authorities.iter().any(|(_, w)| *w == 0)
+	}
+
 	/// Get a genesis set with given authorities.
-	pub(crate) fn genesis(initial: AuthorityList) -> Self {
-		AuthoritySet {
+	pub(crate) fn genesis(initial: AuthorityList) -> Option<Self> {
+		if Self::invalid_authority_list(&initial) {
+			return None;
+		}
+
+		Some(AuthoritySet {
 			current_authorities: initial,
 			set_id: 0,
 			pending_standard_changes: ForkTree::new(),
 			pending_forced_changes: Vec::new(),
+		})
+	}
+
+	/// Create a new authority set.
+	pub(crate) fn new(
+		authorities: AuthorityList,
+		set_id: u64,
+		pending_standard_changes: ForkTree<H, N, PendingChange<H, N>>,
+		pending_forced_changes: Vec<PendingChange<H, N>>,
+	) -> Option<Self> {
+		if Self::invalid_authority_list(&authorities) {
+			return None;
 		}
+
+		Some(AuthoritySet {
+			current_authorities: authorities,
+			set_id,
+			pending_standard_changes,
+			pending_forced_changes,
+		})
 	}
 
 	/// Get the current set id and a reference to the current authority set.
@@ -128,9 +169,9 @@ where
 		&mut self,
 		pending: PendingChange<H, N>,
 		is_descendent_of: &F,
-	) -> Result<(), fork_tree::Error<E>> where
+	) -> Result<(), Error<E>> where
 		F: Fn(&H, &H) -> Result<bool, E>,
-		E:  std::error::Error,
+		E: std::error::Error,
 	{
 		let hash = pending.canon_hash.clone();
 		let number = pending.canon_height.clone();
@@ -159,15 +200,16 @@ where
 		&mut self,
 		pending: PendingChange<H, N>,
 		is_descendent_of: &F,
-	) -> Result<(), fork_tree::Error<E>> where
+	) -> Result<(), Error<E>> where
 		F: Fn(&H, &H) -> Result<bool, E>,
-		E:  std::error::Error,
+		E: std::error::Error,
 	{
 		for change in self.pending_forced_changes.iter() {
 			if change.canon_hash == pending.canon_hash ||
-				is_descendent_of(&change.canon_hash, &pending.canon_hash)?
+				is_descendent_of(&change.canon_hash, &pending.canon_hash)
+					.map_err(fork_tree::Error::Client)?
 			{
-				return Err(fork_tree::Error::UnfinalizedAncestor);
+				return Err(fork_tree::Error::UnfinalizedAncestor.into());
 			}
 		}
 
@@ -201,10 +243,14 @@ where
 		&mut self,
 		pending: PendingChange<H, N>,
 		is_descendent_of: &F,
-	) -> Result<(), fork_tree::Error<E>> where
+	) -> Result<(), Error<E>> where
 		F: Fn(&H, &H) -> Result<bool, E>,
-		E:  std::error::Error,
+		E: std::error::Error,
 	{
+		if Self::invalid_authority_list(&pending.next_authorities) {
+			return Err(Error::InvalidAuthoritySet);
+		}
+
 		match pending.delay_kind {
 			DelayKind::Best { .. } => {
 				self.add_forced_change(pending, is_descendent_of)
@@ -309,9 +355,9 @@ where
 		finalized_number: N,
 		is_descendent_of: &F,
 		initial_sync: bool,
-	) -> Result<Status<H, N>, fork_tree::Error<E>>
-		where F: Fn(&H, &H) -> Result<bool, E>,
-			  E: std::error::Error,
+	) -> Result<Status<H, N>, Error<E>> where
+		F: Fn(&H, &H) -> Result<bool, E>,
+		E: std::error::Error,
 	{
 		let mut status = Status {
 			changed: false,
@@ -370,16 +416,16 @@ where
 		finalized_hash: H,
 		finalized_number: N,
 		is_descendent_of: &F,
-	) -> Result<Option<bool>, fork_tree::Error<E>>
-	where F: Fn(&H, &H) -> Result<bool, E>,
-		  E: std::error::Error,
+	) -> Result<Option<bool>, Error<E>> where
+		F: Fn(&H, &H) -> Result<bool, E>,
+		E: std::error::Error,
 	{
 		self.pending_standard_changes.finalizes_any_with_descendent_if(
 			&finalized_hash,
 			finalized_number.clone(),
 			is_descendent_of,
 			|change| change.effective_number() == finalized_number
-		)
+		).map_err(Error::ForkTree)
 	}
 }
 
@@ -457,8 +503,10 @@ mod tests {
 
 	#[test]
 	fn current_limit_filters_min() {
+		let current_authorities = vec![(AuthorityId::from_slice(&[1; 32]), 1)];
+
 		let mut authorities = AuthoritySet {
-			current_authorities: Vec::new(),
+			current_authorities: current_authorities.clone(),
 			set_id: 0,
 			pending_standard_changes: ForkTree::new(),
 			pending_forced_changes: Vec::new(),
@@ -466,7 +514,7 @@ mod tests {
 
 		let change = |height| {
 			PendingChange {
-				next_authorities: Vec::new(),
+				next_authorities: current_authorities.clone(),
 				delay: 0,
 				canon_height: height,
 				canon_hash: height.to_string(),
@@ -502,15 +550,17 @@ mod tests {
 
 	#[test]
 	fn changes_iterated_in_pre_order() {
+		let current_authorities = vec![(AuthorityId::from_slice(&[1; 32]), 1)];
+
 		let mut authorities = AuthoritySet {
-			current_authorities: Vec::new(),
+			current_authorities: current_authorities.clone(),
 			set_id: 0,
 			pending_standard_changes: ForkTree::new(),
 			pending_forced_changes: Vec::new(),
 		};
 
 		let change_a = PendingChange {
-			next_authorities: Vec::new(),
+			next_authorities: current_authorities.clone(),
 			delay: 10,
 			canon_height: 5,
 			canon_hash: "hash_a",
@@ -518,7 +568,7 @@ mod tests {
 		};
 
 		let change_b = PendingChange {
-			next_authorities: Vec::new(),
+			next_authorities: current_authorities.clone(),
 			delay: 0,
 			canon_height: 5,
 			canon_hash: "hash_b",
@@ -526,7 +576,7 @@ mod tests {
 		};
 
 		let change_c = PendingChange {
-			next_authorities: Vec::new(),
+			next_authorities: current_authorities.clone(),
 			delay: 5,
 			canon_height: 10,
 			canon_hash: "hash_c",
@@ -543,7 +593,7 @@ mod tests {
 
 		// forced changes are iterated last
 		let change_d = PendingChange {
-			next_authorities: Vec::new(),
+			next_authorities: current_authorities.clone(),
 			delay: 2,
 			canon_height: 1,
 			canon_hash: "hash_d",
@@ -551,7 +601,7 @@ mod tests {
 		};
 
 		let change_e = PendingChange {
-			next_authorities: Vec::new(),
+			next_authorities: current_authorities.clone(),
 			delay: 2,
 			canon_height: 0,
 			canon_hash: "hash_e",
@@ -689,7 +739,7 @@ mod tests {
 		// trying to finalize past `change_c` without finalizing `change_a` first
 		assert!(matches!(
 			authorities.apply_standard_changes("hash_d", 40, &is_descendent_of, false),
-			Err(fork_tree::Error::UnfinalizedAncestor)
+			Err(Error::ForkTree(fork_tree::Error::UnfinalizedAncestor))
 		));
 
 		let status = authorities.apply_standard_changes(
@@ -871,4 +921,74 @@ mod tests {
 			}),
 		);
 	}
+
+	#[test]
+	fn maintains_authority_list_invariants() {
+		// empty authority lists are invalid
+		assert_eq!(AuthoritySet::<(), ()>::genesis(vec![]), None);
+		assert_eq!(
+			AuthoritySet::<(), ()>::new(vec![], 0, ForkTree::new(), Vec::new()),
+			None,
+		);
+
+		let invalid_authorities_weight = vec![
+			(AuthorityId::from_slice(&[1; 32]), 5),
+			(AuthorityId::from_slice(&[2; 32]), 0),
+		];
+
+		// authority weight of zero is invalid
+		assert_eq!(
+			AuthoritySet::<(), ()>::genesis(invalid_authorities_weight.clone()),
+			None
+		);
+		assert_eq!(
+			AuthoritySet::<(), ()>::new(
+				invalid_authorities_weight.clone(),
+				0,
+				ForkTree::new(),
+				Vec::new()
+			),
+			None,
+		);
+
+		let mut authority_set =
+			AuthoritySet::<(), u64>::genesis(vec![(AuthorityId::from_slice(&[1; 32]), 5)]).unwrap();
+
+		let invalid_change_empty_authorities = PendingChange {
+			next_authorities: vec![],
+			delay: 10,
+			canon_height: 5,
+			canon_hash: (),
+			delay_kind: DelayKind::Finalized,
+		};
+
+		// pending change contains an empty authority set
+		assert!(matches!(
+			authority_set.add_pending_change(
+				invalid_change_empty_authorities.clone(),
+				&static_is_descendent_of(false)
+			),
+			Err(Error::InvalidAuthoritySet)
+		));
+
+		let invalid_change_authorities_weight = PendingChange {
+			next_authorities: invalid_authorities_weight,
+			delay: 10,
+			canon_height: 5,
+			canon_hash: (),
+			delay_kind: DelayKind::Best {
+				median_last_finalized: 0,
+			},
+		};
+
+		// pending change contains an an authority set
+		// where one authority has weight of 0
+		assert!(matches!(
+			authority_set.add_pending_change(
+				invalid_change_authorities_weight,
+				&static_is_descendent_of(false)
+			),
+			Err(Error::InvalidAuthoritySet)
+		));
+	}
 }
diff --git a/substrate/client/finality-grandpa/src/aux_schema.rs b/substrate/client/finality-grandpa/src/aux_schema.rs
index fe652f52fe..c217bc328a 100644
--- a/substrate/client/finality-grandpa/src/aux_schema.rs
+++ b/substrate/client/finality-grandpa/src/aux_schema.rs
@@ -97,12 +97,14 @@ where H: Clone + Debug + PartialEq,
 			}
 		}
 
-		AuthoritySet {
-			current_authorities: self.current_authorities,
-			set_id: self.set_id,
-			pending_forced_changes: Vec::new(),
-			pending_standard_changes
-		}
+		let authority_set = AuthoritySet::new(
+			self.current_authorities,
+			self.set_id,
+			pending_standard_changes,
+			Vec::new(),
+		);
+
+		authority_set.expect("current_authorities is non-empty and weights are non-zero; qed.")
 	}
 }
 
@@ -334,7 +336,8 @@ pub(crate) fn load_persistent<Block: BlockT, B, G>(
 		from genesis on what appears to be first startup.");
 
 	let genesis_authorities = genesis_authorities()?;
-	let genesis_set = AuthoritySet::genesis(genesis_authorities.clone());
+	let genesis_set = AuthoritySet::genesis(genesis_authorities.clone())
+		.expect("genesis authorities is non-empty; all weights are non-zero; qed.");
 	let state = make_genesis_round();
 	let base = state.prevote_ghost
 		.expect("state is for completed round; completed rounds must have a prevote ghost; qed.");
@@ -503,12 +506,12 @@ mod test {
 
 		assert_eq!(
 			*authority_set.inner().read(),
-			AuthoritySet {
-				current_authorities: authorities.clone(),
-				pending_standard_changes: ForkTree::new(),
-				pending_forced_changes: Vec::new(),
+			AuthoritySet::new(
+				authorities.clone(),
 				set_id,
-			},
+				ForkTree::new(),
+				Vec::new(),
+			).unwrap(),
 		);
 
 		let mut current_rounds = CurrentRounds::new();
@@ -547,12 +550,12 @@ mod test {
 		};
 
 		{
-			let authority_set = AuthoritySet::<H256, u64> {
-				current_authorities: authorities.clone(),
-				pending_standard_changes: ForkTree::new(),
-				pending_forced_changes: Vec::new(),
+			let authority_set = AuthoritySet::<H256, u64>::new(
+				authorities.clone(),
 				set_id,
-			};
+				ForkTree::new(),
+				Vec::new(),
+			).unwrap();
 
 			let voter_set_state = V1VoterSetState::Live(round_number, round_state.clone());
 
@@ -593,12 +596,12 @@ mod test {
 
 		assert_eq!(
 			*authority_set.inner().read(),
-			AuthoritySet {
-				current_authorities: authorities.clone(),
-				pending_standard_changes: ForkTree::new(),
-				pending_forced_changes: Vec::new(),
+			AuthoritySet::new(
+				authorities.clone(),
 				set_id,
-			},
+				ForkTree::new(),
+				Vec::new(),
+			).unwrap(),
 		);
 
 		let mut current_rounds = CurrentRounds::new();
diff --git a/substrate/client/finality-grandpa/src/communication/gossip.rs b/substrate/client/finality-grandpa/src/communication/gossip.rs
index 2d39ed7ec4..afa6581702 100644
--- a/substrate/client/finality-grandpa/src/communication/gossip.rs
+++ b/substrate/client/finality-grandpa/src/communication/gossip.rs
@@ -1618,7 +1618,10 @@ mod tests {
 		use crate::environment::VoterSetState;
 
 		let base = (H256::zero(), 0);
-		let voters = AuthoritySet::genesis(Vec::new());
+
+		let voters = vec![(AuthorityId::from_slice(&[1; 32]), 1)];
+		let voters = AuthoritySet::genesis(voters).unwrap();
+
 		let set_state = VoterSetState::live(
 			0,
 			&voters,
diff --git a/substrate/client/finality-grandpa/src/communication/mod.rs b/substrate/client/finality-grandpa/src/communication/mod.rs
index 7daa121513..c75fe251e7 100644
--- a/substrate/client/finality-grandpa/src/communication/mod.rs
+++ b/substrate/client/finality-grandpa/src/communication/mod.rs
@@ -258,7 +258,7 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 		// is a no-op if currently in that set.
 		self.validator.note_set(
 			set_id,
-			voters.voters().iter().map(|(v, _)| v.clone()).collect(),
+			voters.iter().map(|(v, _)| v.clone()).collect(),
 			|to, neighbor| self.neighbor_sender.send(to, neighbor),
 		);
 
@@ -289,7 +289,7 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 
 		let locals = local_key.and_then(|pair| {
 			let id = pair.public();
-			if voters.contains_key(&id) {
+			if voters.contains(&id) {
 				Some((pair, id))
 			} else {
 				None
@@ -308,12 +308,12 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 					}
 					Ok(GossipMessage::Vote(msg)) => {
 						// check signature.
-						if !voters.contains_key(&msg.message.id) {
+						if !voters.contains(&msg.message.id) {
 							debug!(target: "afg", "Skipping message from unknown voter {}", msg.message.id);
 							return future::ready(None);
 						}
 
-						if voters.len() <= TELEMETRY_VOTERS_LIMIT {
+						if voters.len().get() <= TELEMETRY_VOTERS_LIMIT {
 							match &msg.message.message {
 								PrimaryPropose(propose) => {
 									telemetry!(CONSENSUS_INFO; "afg.received_propose";
@@ -378,7 +378,7 @@ impl<B: BlockT, N: Network<B>> NetworkBridge<B, N> {
 	) {
 		self.validator.note_set(
 			set_id,
-			voters.voters().iter().map(|(v, _)| v.clone()).collect(),
+			voters.iter().map(|(v, _)| v.clone()).collect(),
 			|to, neighbor| self.neighbor_sender.send(to, neighbor),
 		);
 
@@ -476,7 +476,7 @@ fn incoming_global<B: BlockT>(
 		gossip_validator: &Arc<GossipValidator<B>>,
 		voters: &VoterSet<AuthorityId>,
 	| {
-		if voters.len() <= TELEMETRY_VOTERS_LIMIT {
+		if voters.len().get() <= TELEMETRY_VOTERS_LIMIT {
 			let precommits_signed_by: Vec<String> =
 				msg.message.auth_data.iter().map(move |(_, a)| {
 					format!("{}", a)
@@ -799,13 +799,13 @@ fn check_compact_commit<Block: BlockT>(
 ) -> Result<(), ReputationChange> {
 	// 4f + 1 = equivocations from f voters.
 	let f = voters.total_weight() - voters.threshold();
-	let full_threshold = voters.total_weight() + f;
+	let full_threshold = (f + voters.total_weight()).0;
 
 	// check total weight is not out of range.
 	let mut total_weight = 0;
 	for (_, ref id) in &msg.auth_data {
-		if let Some(weight) = voters.info(id).map(|info| info.weight()) {
-			total_weight += weight;
+		if let Some(weight) = voters.get(id).map(|info| info.weight()) {
+			total_weight += weight.get();
 			if total_weight > full_threshold {
 				return Err(cost::MALFORMED_COMMIT);
 			}
@@ -815,7 +815,7 @@ fn check_compact_commit<Block: BlockT>(
 		}
 	}
 
-	if total_weight < voters.threshold() {
+	if total_weight < voters.threshold().get() {
 		return Err(cost::MALFORMED_COMMIT);
 	}
 
@@ -860,7 +860,7 @@ fn check_catch_up<Block: BlockT>(
 ) -> Result<(), ReputationChange> {
 	// 4f + 1 = equivocations from f voters.
 	let f = voters.total_weight() - voters.threshold();
-	let full_threshold = voters.total_weight() + f;
+	let full_threshold = (f + voters.total_weight()).0;
 
 	// check total weight is not out of range for a set of votes.
 	fn check_weight<'a>(
@@ -871,8 +871,8 @@ fn check_catch_up<Block: BlockT>(
 		let mut total_weight = 0;
 
 		for id in votes {
-			if let Some(weight) = voters.info(&id).map(|info| info.weight()) {
-				total_weight += weight;
+			if let Some(weight) = voters.get(&id).map(|info| info.weight()) {
+				total_weight += weight.get();
 				if total_weight > full_threshold {
 					return Err(cost::MALFORMED_CATCH_UP);
 				}
@@ -882,7 +882,7 @@ fn check_catch_up<Block: BlockT>(
 			}
 		}
 
-		if total_weight < voters.threshold() {
+		if total_weight < voters.threshold().get() {
 			return Err(cost::MALFORMED_CATCH_UP);
 		}
 
diff --git a/substrate/client/finality-grandpa/src/communication/tests.rs b/substrate/client/finality-grandpa/src/communication/tests.rs
index ea995eff63..883fdb4f26 100644
--- a/substrate/client/finality-grandpa/src/communication/tests.rs
+++ b/substrate/client/finality-grandpa/src/communication/tests.rs
@@ -29,7 +29,7 @@ use std::{borrow::Cow, pin::Pin, task::{Context, Poll}};
 use crate::environment::SharedVoterSetState;
 use sp_finality_grandpa::{AuthorityList, GRANDPA_ENGINE_ID};
 use super::gossip::{self, GossipValidator};
-use super::{AuthorityId, VoterSet, Round, SetId};
+use super::{VoterSet, Round, SetId};
 
 #[derive(Debug)]
 pub(crate) enum Event {
@@ -142,11 +142,15 @@ fn voter_set_state() -> SharedVoterSetState<Block> {
 	use crate::authorities::AuthoritySet;
 	use crate::environment::VoterSetState;
 	use finality_grandpa::round::State as RoundState;
-	use sp_core::H256;
+	use sp_core::{crypto::Public, H256};
+	use sp_finality_grandpa::AuthorityId;
 
 	let state = RoundState::genesis((H256::zero(), 0));
 	let base = state.prevote_ghost.unwrap();
-	let voters = AuthoritySet::genesis(Vec::new());
+
+	let voters = vec![(AuthorityId::from_slice(&[1; 32]), 1)];
+	let voters = AuthoritySet::genesis(voters).unwrap();
+
 	let set_state = VoterSetState::live(
 		0,
 		&voters,
@@ -212,7 +216,7 @@ impl sc_network_gossip::ValidatorContext<Block> for NoopContext {
 fn good_commit_leads_to_relay() {
 	let private = [Ed25519Keyring::Alice, Ed25519Keyring::Bob, Ed25519Keyring::Charlie];
 	let public = make_ids(&private[..]);
-	let voter_set = Arc::new(public.iter().cloned().collect::<VoterSet<AuthorityId>>());
+	let voter_set = Arc::new(VoterSet::new(public.iter().cloned()).unwrap());
 
 	let round = 1;
 	let set_id = 1;
@@ -360,7 +364,7 @@ fn bad_commit_leads_to_report() {
 	let _ = env_logger::try_init();
 	let private = [Ed25519Keyring::Alice, Ed25519Keyring::Bob, Ed25519Keyring::Charlie];
 	let public = make_ids(&private[..]);
-	let voter_set = Arc::new(public.iter().cloned().collect::<VoterSet<AuthorityId>>());
+	let voter_set = Arc::new(VoterSet::new(public.iter().cloned()).unwrap());
 
 	let round = 1;
 	let set_id = 1;
diff --git a/substrate/client/finality-grandpa/src/environment.rs b/substrate/client/finality-grandpa/src/environment.rs
index cab212333c..1c11c52468 100644
--- a/substrate/client/finality-grandpa/src/environment.rs
+++ b/substrate/client/finality-grandpa/src/environment.rs
@@ -579,23 +579,23 @@ where
 	Block: 'static,
 	B: Backend<Block>,
 	C: crate::ClientForGrandpa<Block, B> + 'static,
- 	N: NetworkT<Block> + 'static + Send,
+	N: NetworkT<Block> + 'static + Send + Sync,
 	SC: SelectChain<Block> + 'static,
 	VR: VotingRule<Block, C>,
 	NumberFor<Block>: BlockNumberOps,
 {
-	type Timer = Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send>>;
+	type Timer = Pin<Box<dyn Future<Output = Result<(), Self::Error>> + Send + Sync>>;
 	type Id = AuthorityId;
 	type Signature = AuthoritySignature;
 
 	// regular round message streams
 	type In = Pin<Box<dyn Stream<
 		Item = Result<::finality_grandpa::SignedMessage<Block::Hash, NumberFor<Block>, Self::Signature, Self::Id>, Self::Error>
-	> + Send>>;
+	> + Send + Sync>>;
 	type Out = Pin<Box<dyn Sink<
 		::finality_grandpa::Message<Block::Hash, NumberFor<Block>>,
 		Error = Self::Error,
-	> + Send>>;
+	> + Send + Sync>>;
 
 	type Error = CommandOrError<Block::Hash, NumberFor<Block>>;
 
diff --git a/substrate/client/finality-grandpa/src/finality_proof.rs b/substrate/client/finality-grandpa/src/finality_proof.rs
index 0eef20d813..c52cc8fc90 100644
--- a/substrate/client/finality-grandpa/src/finality_proof.rs
+++ b/substrate/client/finality-grandpa/src/finality_proof.rs
@@ -54,6 +54,7 @@ use sc_telemetry::{telemetry, CONSENSUS_INFO};
 use sp_finality_grandpa::{AuthorityId, AuthorityList, VersionedAuthorityList, GRANDPA_AUTHORITIES_KEY};
 
 use crate::justification::GrandpaJustification;
+use crate::VoterSet;
 
 /// Maximum number of fragments that we want to return in a single prove_finality call.
 const MAX_FRAGMENTS_IN_PROOF: usize = 8;
@@ -588,7 +589,11 @@ impl<Block: BlockT> ProvableJustification<Block::Header> for GrandpaJustificatio
 		NumberFor<Block>: BlockNumberOps,
 {
 	fn verify(&self, set_id: u64, authorities: &[(AuthorityId, u64)]) -> ClientResult<()> {
-		GrandpaJustification::verify(self, set_id, &authorities.iter().cloned().collect())
+		let authorities = VoterSet::new(authorities.iter().cloned()).ok_or(
+			ClientError::Consensus(sp_consensus::Error::InvalidAuthoritiesSet),
+		)?;
+
+		GrandpaJustification::verify(self, set_id, &authorities)
 	}
 }
 
diff --git a/substrate/client/finality-grandpa/src/lib.rs b/substrate/client/finality-grandpa/src/lib.rs
index 6fab89ac68..be00519f89 100644
--- a/substrate/client/finality-grandpa/src/lib.rs
+++ b/substrate/client/finality-grandpa/src/lib.rs
@@ -674,7 +674,7 @@ pub fn run_grandpa_voter<Block: BlockT, BE: 'static, C, N, SC, VR>(
 		let events = telemetry_on_connect
 			.for_each(move |_| {
 				let curr = authorities.current_authorities();
-				let mut auths = curr.voters().into_iter().map(|(p, _)| p);
+				let mut auths = curr.iter().map(|(p, _)| p);
 				let maybe_authority_id = authority_id(&mut auths, &conf.keystore)
 					.unwrap_or(Default::default());
 
@@ -682,8 +682,8 @@ pub fn run_grandpa_voter<Block: BlockT, BE: 'static, C, N, SC, VR>(
 					"authority_id" => maybe_authority_id.to_string(),
 					"authority_set_id" => ?authorities.set_id(),
 					"authorities" => {
-						let authorities: Vec<String> = curr.voters()
-							.iter().map(|(id, _)| id.to_string()).collect();
+						let authorities: Vec<String> = curr.iter()
+							.map(|(id, _)| id.to_string()).collect();
 						serde_json::to_string(&authorities)
 							.expect("authorities is always at least an empty vector; elements are always of type string")
 					}
@@ -823,7 +823,7 @@ where
 			"authority_id" => authority_id.to_string(),
 			"authority_set_id" => ?self.env.set_id,
 			"authorities" => {
-				let authorities: Vec<String> = self.env.voters.voters()
+				let authorities: Vec<String> = self.env.voters
 					.iter().map(|(id, _)| id.to_string()).collect();
 				serde_json::to_string(&authorities)
 					.expect("authorities is always at least an empty vector; elements are always of type string")
@@ -894,8 +894,16 @@ where
 					Ok(Some(set_state))
 				})?;
 
+				let voters = Arc::new(VoterSet::new(new.authorities.into_iter())
+					.expect("new authorities come from pending change; \
+							 pending change comes from `AuthoritySet`; \
+							 `AuthoritySet` validates authorities is non-empty and weights are non-zero; \
+							 qed."
+					)
+				);
+
 				self.env = Arc::new(Environment {
-					voters: Arc::new(new.authorities.into_iter().collect()),
+					voters,
 					set_id: new.set_id,
 					voter_set_state: self.env.voter_set_state.clone(),
 					// Fields below are simply transferred and not updated.
@@ -1017,7 +1025,8 @@ fn is_voter(
 	keystore: &Option<KeyStorePtr>,
 ) -> Option<AuthorityPair> {
 	match keystore {
-		Some(keystore) => voters.voters().iter()
+		Some(keystore) => voters
+			.iter()
 			.find_map(|(p, _)| keystore.read().key_pair::<AuthorityPair>(&p).ok()),
 		None => None,
 	}
diff --git a/substrate/client/finality-grandpa/src/observer.rs b/substrate/client/finality-grandpa/src/observer.rs
index 1e6c8ddf18..ac67675fef 100644
--- a/substrate/client/finality-grandpa/src/observer.rs
+++ b/substrate/client/finality-grandpa/src/observer.rs
@@ -409,11 +409,13 @@ mod tests {
 			(Arc::new(client), backend)
 		};
 
+		let voters = vec![(sp_keyring::Ed25519Keyring::Alice.public().into(), 1)];
+
 		let persistent_data = aux_schema::load_persistent(
 			&*backend,
 			client.info().genesis_hash,
 			0,
-			|| Ok(vec![]),
+			|| Ok(voters),
 		).unwrap();
 
 		let (_tx, voter_command_rx) = tracing_unbounded("");
diff --git a/substrate/client/finality-grandpa/src/tests.rs b/substrate/client/finality-grandpa/src/tests.rs
index 2821737c4d..5d1c5b2c16 100644
--- a/substrate/client/finality-grandpa/src/tests.rs
+++ b/substrate/client/finality-grandpa/src/tests.rs
@@ -990,7 +990,6 @@ fn test_bad_justification() {
 
 #[test]
 fn voter_persists_its_votes() {
-	use std::iter::FromIterator;
 	use std::sync::atomic::{AtomicUsize, Ordering};
 	use futures::future;
 	use sp_utils::mpsc::{tracing_unbounded, TracingUnboundedReceiver};
@@ -1145,7 +1144,7 @@ fn voter_persists_its_votes() {
 		let (round_rx, round_tx) = network.round_communication(
 			communication::Round(1),
 			communication::SetId(0),
-			Arc::new(VoterSet::from_iter(voters)),
+			Arc::new(VoterSet::new(voters).unwrap()),
 			Some(peers[1].pair().into()),
 			HasVoted::No,
 		);
diff --git a/substrate/client/finality-grandpa/src/until_imported.rs b/substrate/client/finality-grandpa/src/until_imported.rs
index 40da7707b6..737c8c6a77 100644
--- a/substrate/client/finality-grandpa/src/until_imported.rs
+++ b/substrate/client/finality-grandpa/src/until_imported.rs
@@ -147,7 +147,7 @@ pub(crate) struct UntilImported<Block: BlockT, BlockStatus, BlockSyncRequester,
 	inner: Fuse<I>,
 	ready: VecDeque<M::Blocked>,
 	/// Interval at which to check status of each awaited block.
-	check_pending: Pin<Box<dyn Stream<Item = Result<(), std::io::Error>> + Send>>,
+	check_pending: Pin<Box<dyn Stream<Item = Result<(), std::io::Error>> + Send + Sync>>,
 	/// Mapping block hashes to their block number, the point in time it was
 	/// first encountered (Instant) and a list of GRANDPA messages referencing
 	/// the block hash.