diff --git a/substrate/executor/src/native_executor.rs b/substrate/executor/src/native_executor.rs
index 72ba2d33a727d..724c44299f940 100644
--- a/substrate/executor/src/native_executor.rs
+++ b/substrate/executor/src/native_executor.rs
@@ -124,6 +124,8 @@ impl<D: NativeExecutionDispatch + Sync + Send> CodeExecutor for NativeExecutor<D
 				let wasm_module = WasmModule::from_buffer(code)
 					.expect("all modules compiled with rustc are valid wasm code; qed");
 
+				// Missing version export is allowed in Poc-2 for Poc-1 compatibility.
+				// TODO: return an error on missing version.
 				if WasmExecutor.call_in_wasm_module(ext, &wasm_module, "version", &[]).ok()
 					.and_then(|version| RuntimeVersion::decode(&mut version.as_slice()))
 					.map_or(false, |v| D::VERSION.can_call_with(&v))
diff --git a/substrate/network/src/message.rs b/substrate/network/src/message.rs
index b2c44cdf96e8f..3b96b5dae383f 100644
--- a/substrate/network/src/message.rs
+++ b/substrate/network/src/message.rs
@@ -172,6 +172,7 @@ pub mod generic {
 	use codec::Slicable;
 	use runtime_primitives::bft::Justification;
 	use ed25519;
+	use primitives::Signature;
 
 	use super::{Role, BlockAttribute, RemoteCallResponse, RequestId, Transactions, Direction};
 
@@ -207,6 +208,44 @@ pub mod generic {
 		}
 	}
 
+	/// Emulates Poc-1 justification format.
+	#[derive(Clone, PartialEq, Eq, Debug, Serialize, Deserialize)]
+	pub struct V1Justification<H> {
+		/// The round consensus was reached in.
+		pub round_number: u32,
+		/// The hash of the header justified.
+		pub hash: H,
+		/// The signatures and signers of the hash.
+		pub signatures: Vec<([u8; 32], Signature)>
+	}
+
+	// TODO: remove this after poc-2
+	/// Justification back compat
+	#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
+	#[serde(untagged)]
+	pub enum BlockJustification<H> {
+		/// Poc-1 format.
+		V1(V1Justification<H>),
+		/// Poc-2 format.
+		V2(Justification<H>),
+	}
+
+	impl<H> BlockJustification<H> {
+		/// Convert to PoC-2 justification format.
+		pub fn to_justification(self) -> Justification<H> {
+			match self {
+				BlockJustification::V2(j) => j,
+				BlockJustification::V1(j) => {
+					Justification {
+						round_number: j.round_number,
+						hash: j.hash,
+						signatures: j.signatures.into_iter().map(|(a, s)| (a.into(), s)).collect(),
+					}
+				}
+			}
+		}
+	}
+
 	/// Block data sent in the response.
 	#[derive(Debug, PartialEq, Eq, Clone, Serialize, Deserialize)]
 	pub struct BlockData<Header, Hash, Extrinsic> {
@@ -221,7 +260,7 @@ pub mod generic {
 		/// Block message queue if requested.
 		pub message_queue: Option<Vec<u8>>,
 		/// Justification if requested.
-		pub justification: Option<Justification<Hash>>,
+		pub justification: Option<BlockJustification<Hash>>,
 	}
 
 	/// Identifies starting point of a block sequence.
diff --git a/substrate/network/src/protocol.rs b/substrate/network/src/protocol.rs
index 6d23f1c7bd864..d46ff839c3f85 100644
--- a/substrate/network/src/protocol.rs
+++ b/substrate/network/src/protocol.rs
@@ -142,7 +142,8 @@ impl<B: BlockT> Protocol<B> where
 		let message: Message<B> = match serde_json::from_slice(data) {
 			Ok(m) => m,
 			Err(e) => {
-				debug!("Invalid packet from {}: {}", peer_id, e);
+				debug!(target: "sync", "Invalid packet from {}: {}", peer_id, e);
+				trace!(target: "sync", "Invalid packet: {}", String::from_utf8_lossy(data));
 				io.disable_peer(peer_id);
 				return;
 			}
@@ -159,13 +160,13 @@ impl<B: BlockT> Protocol<B> where
 						match mem::replace(&mut peer.block_request, None) {
 							Some(r) => r,
 							None => {
-								debug!("Unexpected response packet from {}", peer_id);
+								debug!(target: "sync", "Unexpected response packet from {}", peer_id);
 								io.disable_peer(peer_id);
 								return;
 							}
 						}
 					} else {
-						debug!("Unexpected packet from {}", peer_id);
+						debug!(target: "sync", "Unexpected packet from {}", peer_id);
 						io.disable_peer(peer_id);
 						return;
 					}
@@ -259,13 +260,14 @@ impl<B: BlockT> Protocol<B> where
 			}
 			let number = header.number().clone();
 			let hash = header.hash();
+			let justification = if get_justification { self.chain.justification(&BlockId::Hash(hash)).unwrap_or(None) } else { None };
 			let block_data = message::generic::BlockData {
 				hash: hash,
 				header: if get_header { Some(header) } else { None },
 				body: (if get_body { self.chain.body(&BlockId::Hash(hash)).unwrap_or(None) } else { None }).map(|body| message::Body::Extrinsics(body)),
 				receipt: None,
 				message_queue: None,
-				justification: if get_justification { self.chain.justification(&BlockId::Hash(hash)).unwrap_or(None) } else { None },
+				justification: justification.map(|j| message::generic::BlockJustification::V2(j)),
 			};
 			blocks.push(block_data);
 			match request.direction {
diff --git a/substrate/network/src/sync.rs b/substrate/network/src/sync.rs
index 8a296d4534f4f..e75fcd16f9d57 100644
--- a/substrate/network/src/sync.rs
+++ b/substrate/network/src/sync.rs
@@ -258,7 +258,7 @@ impl<B: BlockT> ChainSync<B> where
 					let result = protocol.chain().import(
 						is_best,
 						header,
-						justification,
+						justification.to_justification(),
 						block.body.map(|b| b.to_extrinsics()),
 					);
 					match result {