diff --git a/substrate/core/finality-grandpa/src/communication.rs b/substrate/core/finality-grandpa/src/communication.rs
index 926b0e01e2..9d661ae31b 100644
--- a/substrate/core/finality-grandpa/src/communication.rs
+++ b/substrate/core/finality-grandpa/src/communication.rs
@@ -32,25 +32,31 @@ fn localized_payload<E: Encode>(round: u64, set_id: u64, message: &E) -> Vec<u8>
 	(message, round, set_id).encode()
 }
 
-enum Broadcast {
+enum Broadcast<Block: BlockT> {
 	// set_id, round, encoded commit.
 	Commit(u64, u64, Vec<u8>),
 	// set_id, round, encoded signed message.
 	Message(u64, u64, Vec<u8>),
+	// set_id, round, announcement of block hash that should be downloaded
+	Announcement(u64, u64, Block::Hash),
+	// set_id, round being dropped.
+	DropRound(u64, u64),
 }
 
-impl Broadcast {
+impl<Block: BlockT> Broadcast<Block> {
 	fn set_id(&self) -> u64 {
 		match *self {
 			Broadcast::Commit(s, _, _) => s,
 			Broadcast::Message(s, _, _) => s,
+			Broadcast::Announcement(s, _, _) => s,
+			Broadcast::DropRound(s, _) => s,
 		}
 	}
 }
 
 /// Produces a future that should be run in the background and proxies
 /// and rebroadcasts messages.
-pub(crate) fn rebroadcasting_network<N: Network>(network: N) -> (BroadcastWorker<N>, BroadcastHandle<N>) {
+pub(crate) fn rebroadcasting_network<B: BlockT, N: Network<B>>(network: N) -> (BroadcastWorker<B, N>, BroadcastHandle<B, N>) {
 	use std::time::Duration;
 	const REBROADCAST_PERIOD: Duration = Duration::from_secs(60);
 
@@ -62,6 +68,7 @@ pub(crate) fn rebroadcasting_network<N: Network>(network: N) -> (BroadcastWorker
 			set_id: 0, // will be overwritten on first item to broadcast.
 			last_commit: None,
 			round_messages: (0, Vec::new()),
+			announcements: HashMap::new(),
 			network: network.clone(),
 			incoming_broadcast: rx,
 		},
@@ -75,23 +82,24 @@ pub(crate) fn rebroadcasting_network<N: Network>(network: N) -> (BroadcastWorker
 // A worker which broadcasts messages to the background, potentially
 // rebroadcasting.
 #[must_use = "network rebroadcast future must be driven to completion"]
-pub(crate) struct BroadcastWorker<N: Network> {
+pub(crate) struct BroadcastWorker<B: BlockT, N: Network<B>> {
 	interval: Interval,
 	set_id: u64,
 	last_commit: Option<(u64, Vec<u8>)>,
 	round_messages: (u64, Vec<Vec<u8>>),
+	announcements: HashMap<B::Hash, u64>,
 	network: N,
-	incoming_broadcast: mpsc::UnboundedReceiver<Broadcast>,
+	incoming_broadcast: mpsc::UnboundedReceiver<Broadcast<B>>,
 }
 
 /// A handle used by communication work to broadcast to network.
 #[derive(Clone)]
-pub(crate) struct BroadcastHandle<N> {
-	relay: mpsc::UnboundedSender<Broadcast>,
+pub(crate) struct BroadcastHandle<B: BlockT, N> {
+	relay: mpsc::UnboundedSender<Broadcast<B>>,
 	network: N,
 }
 
-impl<N: Network> Future for BroadcastWorker<N> {
+impl<B: BlockT, N: Network<B>> Future for BroadcastWorker<B, N> {
 	type Item = ();
 	type Error = Error;
 
@@ -114,6 +122,10 @@ impl<N: Network> Future for BroadcastWorker<N> {
 				for message in self.round_messages.1.iter().cloned() {
 					self.network.send_message(round, self.set_id, message);
 				}
+
+				for (&announce_hash, &round) in &self.announcements {
+					self.network.announce(round, self.set_id, announce_hash);
+				}
 			}
 		}
 		loop {
@@ -127,6 +139,7 @@ impl<N: Network> Future for BroadcastWorker<N> {
 						self.set_id = item.set_id();
 						self.last_commit = None;
 						self.round_messages = (0, Vec::new());
+						self.announcements.clear();
 					}
 
 					match item {
@@ -154,6 +167,19 @@ impl<N: Network> Future for BroadcastWorker<N> {
 							// always send out to network.
 							self.network.send_message(round, set_id, message);
 						}
+						Broadcast::Announcement(set_id, round, hash) => {
+							if self.set_id == set_id {
+								self.announcements.insert(hash, round);
+							}
+
+							// always send out.
+							self.network.announce(round, set_id, hash);
+						}
+						Broadcast::DropRound(set_id, round) => {
+							// stop making announcements for any dead rounds.
+							self.announcements.retain(|_, &mut r| r > round);
+							self.network.drop_messages(round, set_id);
+						}
 					}
 				}
 			}
@@ -161,7 +187,7 @@ impl<N: Network> Future for BroadcastWorker<N> {
 	}
 }
 
-impl<N: Network> Network for BroadcastHandle<N> {
+impl<B: BlockT, N: Network<B>> Network<B> for BroadcastHandle<B, N> {
 	type In = N::In;
 
 	fn messages_for(&self, round: u64, set_id: u64) -> Self::In {
@@ -173,7 +199,7 @@ impl<N: Network> Network for BroadcastHandle<N> {
 	}
 
 	fn drop_messages(&self, round: u64, set_id: u64) {
-		self.network.drop_messages(round, set_id);
+		let _ = self.relay.unbounded_send(Broadcast::DropRound(set_id, round));
 	}
 
 	fn commit_messages(&self, set_id: u64) -> Self::In {
@@ -183,6 +209,10 @@ impl<N: Network> Network for BroadcastHandle<N> {
 	fn send_commit(&self, round: u64, set_id: u64, message: Vec<u8>) {
 		let _ = self.relay.unbounded_send(Broadcast::Commit(round, set_id, message));
 	}
+
+	fn announce(&self, round: u64, set_id: u64, block: B::Hash) {
+		let _ = self.relay.unbounded_send(Broadcast::Announcement(round, set_id, block));
+	}
 }
 
 // check a message.
@@ -243,7 +273,7 @@ pub(crate) fn checked_message_stream<Block: BlockT, S>(
 		.map_err(|()| Error::Network(format!("Failed to receive message on unbounded stream")))
 }
 
-struct OutgoingMessages<Block: BlockT, N: Network> {
+pub(crate) struct OutgoingMessages<Block: BlockT, N: Network<Block>> {
 	round: u64,
 	set_id: u64,
 	locals: Option<(Arc<ed25519::Pair>, Ed25519AuthorityId)>,
@@ -251,7 +281,8 @@ struct OutgoingMessages<Block: BlockT, N: Network> {
 	network: N,
 }
 
-impl<Block: BlockT, N: Network> Sink for OutgoingMessages<Block, N> {
+impl<Block: BlockT, N: Network<Block>> Sink for OutgoingMessages<Block, N>
+{
 	type SinkItem = Message<Block>;
 	type SinkError = Error;
 
@@ -260,14 +291,20 @@ impl<Block: BlockT, N: Network> Sink for OutgoingMessages<Block, N> {
 		if let Some((ref pair, local_id)) = self.locals {
 			let encoded = localized_payload(self.round, self.set_id, &msg);
 			let signature = pair.sign(&encoded[..]);
+
+			let target_hash = msg.target().0.clone();
 			let signed = SignedMessage::<Block> {
 				message: msg,
 				signature,
 				id: local_id,
 			};
 
-			// forward to network and to inner sender.
+			// announce our block hash to peers and propagate the
+			// message.
+			self.network.announce(self.round, self.set_id, target_hash);
 			self.network.send_message(self.round, self.set_id, signed.encode());
+
+			// forward the message to the inner sender.
 			let _ = self.sender.unbounded_send(signed);
 		}
 
@@ -282,7 +319,7 @@ impl<Block: BlockT, N: Network> Sink for OutgoingMessages<Block, N> {
 	}
 }
 
-impl<Block: BlockT, N: Network> Drop for OutgoingMessages<Block, N> {
+impl<Block: BlockT, N: Network<Block>> Drop for OutgoingMessages<Block, N> {
 	fn drop(&mut self) {
 		self.network.drop_messages(self.round, self.set_id);
 	}
@@ -293,7 +330,7 @@ impl<Block: BlockT, N: Network> Drop for OutgoingMessages<Block, N> {
 ///
 /// A future can push unsigned messages into the sink. They will be automatically
 /// broadcast to the network. The returned stream should be combined with other input.
-pub(crate) fn outgoing_messages<Block: BlockT, N: Network>(
+pub(crate) fn outgoing_messages<Block: BlockT, N: Network<Block>>(
 	round: u64,
 	set_id: u64,
 	local_key: Option<Arc<ed25519::Pair>>,
@@ -301,7 +338,7 @@ pub(crate) fn outgoing_messages<Block: BlockT, N: Network>(
 	network: N,
 ) -> (
 	impl Stream<Item=SignedMessage<Block>,Error=Error>,
-	impl Sink<SinkItem=Message<Block>,SinkError=Error>,
+	OutgoingMessages<Block, N>,
 ) {
 	let locals = local_key.and_then(|pair| {
 		let public = pair.public();
@@ -410,7 +447,7 @@ impl<Block, N> CommitsOut<Block, N> {
 	}
 }
 
-impl<Block: BlockT, N: Network> Sink for CommitsOut<Block, N> {
+impl<Block: BlockT, N: Network<Block>> Sink for CommitsOut<Block, N> {
 	type SinkItem = (u64, Commit<Block>);
 	type SinkError = Error;
 
diff --git a/substrate/core/finality-grandpa/src/lib.rs b/substrate/core/finality-grandpa/src/lib.rs
index ddf3874546..d84cf00728 100644
--- a/substrate/core/finality-grandpa/src/lib.rs
+++ b/substrate/core/finality-grandpa/src/lib.rs
@@ -219,7 +219,7 @@ impl From<ClientError> for Error {
 /// handle to a gossip service or similar.
 ///
 /// Intended to be a lightweight handle such as an `Arc`.
-pub trait Network: Clone {
+pub trait Network<Block: BlockT>: Clone {
 	/// A stream of input messages for a topic.
 	type In: Stream<Item=Vec<u8>,Error=()>;
 
@@ -239,6 +239,9 @@ pub trait Network: Clone {
 
 	/// Send message over the commit channel.
 	fn send_commit(&self, round: u64, set_id: u64, message: Vec<u8>);
+
+	/// Inform peers that a block with given hash should be downloaded.
+	fn announce(&self, round: u64, set_id: u64, block: Block::Hash);
 }
 
 ///  Bridge between NetworkService, gossiping consensus messages and Grandpa
@@ -269,7 +272,7 @@ fn commit_topic<B: BlockT>(set_id: u64) -> B::Hash {
 	<<B::Header as HeaderT>::Hashing as HashT>::hash(format!("{}-COMMITS", set_id).as_bytes())
 }
 
-impl<B: BlockT, S: network::specialization::NetworkSpecialization<B>, H: ExHashT> Network for NetworkBridge<B, S, H> {
+impl<B: BlockT, S: network::specialization::NetworkSpecialization<B>, H: ExHashT> Network<B> for NetworkBridge<B, S, H> {
 	type In = mpsc::UnboundedReceiver<ConsensusMessage>;
 	fn messages_for(&self, round: u64, set_id: u64) -> Self::In {
 		self.service.consensus_gossip().write().messages_for(message_topic::<B>(round, set_id))
@@ -293,6 +296,11 @@ impl<B: BlockT, S: network::specialization::NetworkSpecialization<B>, H: ExHashT
 		let topic = commit_topic::<B>(set_id);
 		self.service.gossip_consensus_message(topic, message, true);
 	}
+
+	fn announce(&self, round: u64, _set_id: u64, block: B::Hash) {
+		debug!(target: "afg", "Announcing block {} to peers which we voted on in round {}", block, round);
+		self.service.announce_block(block)
+	}
 }
 
 /// Something which can determine if a block is known.
@@ -368,7 +376,7 @@ impl<H: Copy + PartialEq, N: Copy + Ord> ConsensusChanges<H, N> {
 type SharedConsensusChanges<H, N> = Arc<parking_lot::Mutex<ConsensusChanges<H, N>>>;
 
 /// The environment we run GRANDPA in.
-struct Environment<B, E, Block: BlockT, N: Network, RA> {
+struct Environment<B, E, Block: BlockT, N: Network<Block>, RA> {
 	inner: Arc<Client<B, E, Block, RA>>,
 	voters: Arc<VoterSet<Ed25519AuthorityId>>,
 	config: Config,
@@ -382,7 +390,7 @@ impl<Block: BlockT<Hash=H256>, B, E, N, RA> grandpa::Chain<Block::Hash, NumberFo
 	Block: 'static,
 	B: Backend<Block, Blake2Hasher> + 'static,
 	E: CallExecutor<Block, Blake2Hasher> + 'static,
-	N: Network + 'static,
+	N: Network<Block> + 'static,
 	N::In: 'static,
 	NumberFor<Block>: BlockNumberOps,
 {
@@ -540,7 +548,7 @@ impl<B, E, Block: BlockT<Hash=H256>, N, RA> voter::Environment<Block::Hash, Numb
 	Block: 'static,
 	B: Backend<Block, Blake2Hasher> + 'static,
 	E: CallExecutor<Block, Blake2Hasher> + 'static + Send + Sync,
-	N: Network + 'static + Send,
+	N: Network<Block> + 'static + Send,
 	N::In: 'static + Send,
 	RA: 'static + Send + Sync,
 	NumberFor<Block>: BlockNumberOps,
@@ -1476,7 +1484,7 @@ fn committer_communication<Block: BlockT<Hash=H256>, B, E, N, RA>(
 ) where
 	B: Backend<Block, Blake2Hasher>,
 	E: CallExecutor<Block, Blake2Hasher> + Send + Sync,
-	N: Network,
+	N: Network<Block>,
 	RA: Send + Sync,
 	NumberFor<Block>: BlockNumberOps,
 	DigestItemFor<Block>: DigestItem<AuthorityId=Ed25519AuthorityId>,
@@ -1522,7 +1530,7 @@ pub fn run_grandpa<B, E, Block: BlockT<Hash=H256>, N, RA>(
 	Block::Hash: Ord,
 	B: Backend<Block, Blake2Hasher> + 'static,
 	E: CallExecutor<Block, Blake2Hasher> + Send + Sync + 'static,
-	N: Network + Send + Sync + 'static,
+	N: Network<Block> + Send + Sync + 'static,
 	N::In: Send + 'static,
 	NumberFor<Block>: BlockNumberOps,
 	DigestFor<Block>: Encode,
diff --git a/substrate/core/finality-grandpa/src/tests.rs b/substrate/core/finality-grandpa/src/tests.rs
index 61147a4b22..1e2b25ad4b 100644
--- a/substrate/core/finality-grandpa/src/tests.rs
+++ b/substrate/core/finality-grandpa/src/tests.rs
@@ -175,7 +175,7 @@ fn make_commit_topic(set_id: u64) -> Hash {
 	hash
 }
 
-impl Network for MessageRouting {
+impl Network<Block> for MessageRouting {
 	type In = Box<Stream<Item=Vec<u8>,Error=()> + Send>;
 
 	fn messages_for(&self, round: u64, set_id: u64) -> Self::In {
@@ -229,6 +229,10 @@ impl Network for MessageRouting {
 		inner.peer(self.peer_id).gossip_message(make_commit_topic(set_id), message, true);
 		inner.route_until_complete();
 	}
+
+	fn announce(&self, _round: u64, _set_id: u64, _block: H256) {
+
+	}
 }
 
 #[derive(Default, Clone)]
diff --git a/substrate/core/network/src/protocol.rs b/substrate/core/network/src/protocol.rs
index d31bf43716..02b2ff7963 100644
--- a/substrate/core/network/src/protocol.rs
+++ b/substrate/core/network/src/protocol.rs
@@ -686,6 +686,34 @@ impl<B: BlockT, S: NetworkSpecialization<B>, H: ExHashT> Protocol<B, S, H> {
 		self.transaction_pool.on_broadcasted(propagated_to);
 	}
 
+	/// Make sure an important block is propagated to peers.
+	///
+	/// In chain-based consensus, we often need to make sure non-best forks are
+	/// at least temporarily synced.
+	pub fn announce_block(&self, io: &mut SyncIo, hash: B::Hash) {
+		let header = match self.context_data.chain.header(&BlockId::Hash(hash)) {
+			Ok(Some(header)) => header,
+			Ok(None) => {
+				warn!("Trying to announce unknown block: {}", hash);
+				return;
+			}
+			Err(e) => {
+				warn!("Error reading block header {}: {:?}", hash, e);
+				return;
+			}
+		};
+		let mut peers = self.context_data.peers.write();
+		let hash = header.hash();
+		for (who, ref mut peer) in peers.iter_mut() {
+			if peer.known_blocks.insert(hash.clone()) {
+				trace!(target: "sync", "Reannouncing block {:?} to {}", hash, who);
+				self.send_message(io, *who, GenericMessage::BlockAnnounce(message::BlockAnnounce {
+					header: header.clone()
+				}));
+			}
+		}
+	}
+
 	/// Send Status message
 	fn send_status(&self, io: &mut SyncIo, who: NodeIndex) {
 		if let Ok(info) = self.context_data.chain.info() {
diff --git a/substrate/core/network/src/service.rs b/substrate/core/network/src/service.rs
index 91840063b2..05b455aead 100644
--- a/substrate/core/network/src/service.rs
+++ b/substrate/core/network/src/service.rs
@@ -200,6 +200,14 @@ impl<B: BlockT + 'static, S: NetworkSpecialization<B>, H: ExHashT> Service<B, S,
 		self.handler.propagate_extrinsics(&mut NetSyncIo::new(&self.network, self.protocol_id));
 	}
 
+	/// Make sure an important block is propagated to peers.
+	///
+	/// In chain-based consensus, we often need to make sure non-best forks are
+	/// at least temporarily synced.
+	pub fn announce_block(&self, hash: B::Hash) {
+		self.handler.announce_block(&mut NetSyncIo::new(&self.network, self.protocol_id), hash);
+	}
+
 	/// Send a consensus message through the gossip
 	pub fn gossip_consensus_message(&self, topic: B::Hash, message: Vec<u8>, broadcast: bool) {
 		self.handler.gossip_consensus_message(
diff --git a/substrate/core/network/src/sync.rs b/substrate/core/network/src/sync.rs
index 629e8e3d1b..dcb38d7829 100644
--- a/substrate/core/network/src/sync.rs
+++ b/substrate/core/network/src/sync.rs
@@ -38,12 +38,15 @@ const MAX_IMPORTING_BLOCKS: usize = 2048;
 const MAJOR_SYNC_BLOCKS: usize = 5;
 // Time to wait before trying to get a justification from the same peer.
 const JUSTIFICATION_RETRY_WAIT: Duration = Duration::from_secs(10);
+// Number of recently announced blocks to track for each peer.
+const ANNOUNCE_HISTORY_SIZE: usize = 64;
 
 struct PeerSync<B: BlockT> {
 	pub common_number: NumberFor<B>,
 	pub best_hash: B::Hash,
 	pub best_number: NumberFor<B>,
 	pub state: PeerSyncState<B>,
+	pub recently_announced: VecDeque<B::Hash>,
 }
 
 #[derive(Copy, Clone, Eq, PartialEq, Debug)]
@@ -334,6 +337,7 @@ impl<B: BlockT> ChainSync<B> {
 						best_hash: info.best_hash,
 						best_number: info.best_number,
 						state: PeerSyncState::Available,
+						recently_announced: Default::default(),
 					});
 				}
 				(Ok(BlockStatus::Unknown), _) => {
@@ -346,6 +350,7 @@ impl<B: BlockT> ChainSync<B> {
 							best_hash: info.best_hash,
 							best_number: info.best_number,
 							state: PeerSyncState::AncestorSearch(common_best),
+							recently_announced: Default::default(),
 						});
 						Self::request_ancestry(protocol, who, common_best)
 					} else {
@@ -356,6 +361,7 @@ impl<B: BlockT> ChainSync<B> {
 							best_hash: info.best_hash,
 							best_number: info.best_number,
 							state: PeerSyncState::Available,
+							recently_announced: Default::default(),
 						});
 						self.download_new(protocol, who)
 					}
@@ -367,6 +373,7 @@ impl<B: BlockT> ChainSync<B> {
 						best_hash: info.best_hash,
 						best_number: info.best_number,
 						state: PeerSyncState::Available,
+						recently_announced: Default::default(),
 					});
 				}
 			}
@@ -457,13 +464,16 @@ impl<B: BlockT> ChainSync<B> {
 			Vec::new()
 		};
 
-		let best_seen = self.best_seen_block();
-		let is_best = new_blocks.first().and_then(|b| b.header.as_ref()).map(|h| best_seen.as_ref().map_or(false, |n| h.number() >= n));
-		let origin = if is_best.unwrap_or_default() { BlockOrigin::NetworkBroadcast } else { BlockOrigin::NetworkInitialSync };
+		let is_recent = new_blocks
+			.first()
+			.map(|block| self.peers.iter().any(|(_, peer)| peer.recently_announced.contains(&block.hash)))
+			.unwrap_or(false);
+		let origin = if is_recent { BlockOrigin::NetworkBroadcast } else { BlockOrigin::NetworkInitialSync };
 
 		if let Some((hash, number)) = new_blocks.last()
 			.and_then(|b| b.header.as_ref().map(|h| (b.hash.clone(), *h.number())))
 		{
+			trace!(target:"sync", "Accepted {} blocks ({:?}) with origin {:?}", new_blocks.len(), hash, origin);
 			self.block_queued(&hash, number);
 		}
 		self.maintain_sync(protocol);
@@ -586,6 +596,10 @@ impl<B: BlockT> ChainSync<B> {
 		let known_parent = self.is_known(protocol, &header.parent_hash());
 		let known = self.is_known(protocol, &hash);
 		if let Some(ref mut peer) = self.peers.get_mut(&who) {
+			while peer.recently_announced.len() >= ANNOUNCE_HISTORY_SIZE {
+				peer.recently_announced.pop_front();
+			}
+			peer.recently_announced.push_back(hash.clone());
 			if number > peer.best_number {
 				// update their best block
 				peer.best_number = number;