diff --git a/substrate/candidate-agreement/src/bft/mod.rs b/substrate/candidate-agreement/src/bft/mod.rs
index 5c6b126a1e..6beff362e4 100644
--- a/substrate/candidate-agreement/src/bft/mod.rs
+++ b/substrate/candidate-agreement/src/bft/mod.rs
@@ -308,16 +308,17 @@ impl<C: Context> Strategy<C> {
 	) {
 		// TODO: find a way to avoid processing of the signatures if the sender is
 		// not the primary or the round number is low.
-		let current_round_number = self.current_accumulator.round_number();
-		if justification.round_number < current_round_number {
-			return
-		} else if justification.round_number == current_round_number {
-			self.locked = Some(Locked { justification });
-		} else {
+		if justification.round_number > self.current_accumulator.round_number() {
 			// jump ahead to the prior round as this is an indication of a supermajority
 			// good nodes being at least on that round.
 			self.advance_to_round(context, justification.round_number);
-			self.locked = Some(Locked { justification });
+		}
+
+		let lock_to_new = self.locked.as_ref()
+			.map_or(true, |l| l.justification.round_number < justification.round_number);
+
+		if lock_to_new {
+			self.locked = Some(Locked { justification })
 		}
 	}
 
diff --git a/substrate/candidate-agreement/src/bft/tests.rs b/substrate/candidate-agreement/src/bft/tests.rs
index 165166d76a..86857ba5de 100644
--- a/substrate/candidate-agreement/src/bft/tests.rs
+++ b/substrate/candidate-agreement/src/bft/tests.rs
@@ -322,3 +322,91 @@ fn consensus_does_not_complete_without_enough_nodes() {
 
 	assert!(result.is_none(), "not enough online nodes");
 }
+
+#[test]
+fn threshold_plus_one_locked_on_proposal_only_one_with_candidate() {
+	let node_count = 10;
+	let max_faulty = 3;
+
+	let locked_proposal = Candidate(999_999_999);
+	let locked_digest = Digest(999_999_999);
+	let locked_round = 1;
+	let justification = PrepareJustification {
+		round_number: locked_round,
+		digest: locked_digest.clone(),
+		signatures: (0..7)
+			.map(|i| Signature(Message::Prepare(locked_round, locked_digest.clone()), ValidatorId(i)))
+			.collect()
+	};
+
+	let mut shared_context = SharedContext::new(node_count);
+	shared_context.current_round = locked_round + 1;
+	let shared_context = Arc::new(Mutex::new(shared_context));
+
+	let (network, net_send, net_recv) = Network::new(node_count);
+	network.route_on_thread();
+
+	let nodes = net_send
+		.into_iter()
+		.zip(net_recv)
+		.enumerate()
+		.map(|(i, (tx, rx))| {
+			let ctx = TestContext {
+				local_id: ValidatorId(i),
+				proposal: Mutex::new(i),
+				shared: shared_context.clone(),
+			};
+
+			let mut agreement = agree(
+				ctx,
+				node_count,
+				max_faulty,
+				rx.map_err(|_| Error),
+				tx.sink_map_err(|_| Error).with(move |t| Ok((i, t))),
+			);
+
+			agreement.strategy.advance_to_round(
+				&agreement.context,
+				locked_round + 1
+			);
+
+			if i <= max_faulty {
+				agreement.strategy.locked = Some(Locked {
+					justification: justification.clone(),
+				})
+			}
+
+			if i == max_faulty {
+				agreement.strategy.notable_candidates.insert(
+					locked_digest.clone(),
+					locked_proposal.clone(),
+				);
+			}
+
+			agreement
+		})
+		.collect::<Vec<_>>();
+
+	::std::thread::spawn(move || {
+		let mut timeout = ::std::time::Duration::from_millis(50);
+		loop {
+			::std::thread::sleep(timeout.clone());
+			shared_context.lock().unwrap().bump_round();
+			timeout *= 2;
+		}
+	});
+
+	let timeout = timeout_in(Duration::from_millis(500)).map_err(|_| Error);
+	let results = ::futures::future::join_all(nodes)
+		.map(Some)
+		.select(timeout.map(|_| None))
+		.wait()
+		.map(|(i, _)| i)
+		.map_err(|(e, _)| e)
+		.expect("to complete")
+		.expect("to not time out");
+
+	for result in &results {
+		assert_eq!(&result.justification.digest, &locked_digest);
+	}
+}