diff --git a/ethcore/light/src/client/mod.rs b/ethcore/light/src/client/mod.rs
index a113b4367..bebe89e0e 100644
--- a/ethcore/light/src/client/mod.rs
+++ b/ethcore/light/src/client/mod.rs
@@ -20,7 +20,7 @@ use std::sync::Arc;
 
 use ethcore::block_import_error::BlockImportError;
 use ethcore::block_status::BlockStatus;
-use ethcore::client::ClientReport;
+use ethcore::client::{ClientReport, EnvInfo};
 use ethcore::engines::Engine;
 use ethcore::ids::BlockId;
 use ethcore::header::Header;
@@ -62,6 +62,9 @@ pub trait LightChainClient: Send + Sync {
 	/// Get the best block header.
 	fn best_block_header(&self) -> encoded::Header;
 
+	/// Get the signing network ID.
+	fn signing_network_id(&self) -> Option<u64>;
+
 	/// Query whether a block is known.
 	fn is_known(&self, hash: &H256) -> bool;
 
@@ -164,6 +167,11 @@ impl Client {
 		self.chain.best_header()
 	}
 
+	/// Get the signing network id.
+	pub fn signing_network_id(&self) -> Option<u64> {
+		self.engine.signing_network_id(&self.latest_env_info())
+	}
+
 	/// Flush the header queue.
 	pub fn flush_queue(&self) {
 		self.queue.flush()
@@ -217,6 +225,33 @@ impl Client {
 	pub fn engine(&self) -> &Engine {
 		&*self.engine
 	}
+
+	fn latest_env_info(&self) -> EnvInfo {
+		let header = self.best_block_header();
+
+		EnvInfo {
+			number: header.number(),
+			author: header.author(),
+			timestamp: header.timestamp(),
+			difficulty: header.difficulty(),
+			last_hashes: self.build_last_hashes(header.hash()),
+			gas_used: Default::default(),
+			gas_limit: header.gas_limit(),
+		}
+	}
+
+	fn build_last_hashes(&self, mut parent_hash: H256) -> Arc<Vec<H256>> {
+		let mut v = Vec::with_capacity(256);
+		for _ in 0..255 {
+			v.push(parent_hash);
+			match self.block_header(BlockId::Hash(parent_hash)) {
+				Some(header) => parent_hash = header.hash(),
+				None => break,
+			}
+		}
+
+		Arc::new(v)
+	}
 }
 
 impl LightChainClient for Client {
@@ -234,6 +269,10 @@ impl LightChainClient for Client {
 		Client::best_block_header(self)
 	}
 
+	fn signing_network_id(&self) -> Option<u64> {
+		Client::signing_network_id(self)
+	}
+
 	fn is_known(&self, hash: &H256) -> bool {
 		self.status(hash) == BlockStatus::InChain
 	}
diff --git a/rpc/src/v1/helpers/dispatch.rs b/rpc/src/v1/helpers/dispatch.rs
index de0207d79..e8fbf9b76 100644
--- a/rpc/src/v1/helpers/dispatch.rs
+++ b/rpc/src/v1/helpers/dispatch.rs
@@ -207,7 +207,7 @@ impl Dispatcher for LightDispatcher {
 	fn sign(&self, accounts: Arc<AccountProvider>, filled: FilledTransactionRequest, password: SignWith)
 		-> BoxFuture<WithToken<SignedTransaction>, Error>
 	{
-		let network_id = None; // TODO: fetch from client.
+		let network_id = self.client.signing_network_id();
 		let address = filled.from;
 		let best_header = self.client.best_block_header();