diff --git a/ethcore/res/ethereum/classic.json b/ethcore/res/ethereum/classic.json
index 223978ca4..c1879d459 100644
--- a/ethcore/res/ethereum/classic.json
+++ b/ethcore/res/ethereum/classic.json
@@ -27,6 +27,7 @@
 		"maximumExtraDataSize": "0x20",
 		"minGasLimit": "0x1388",
 		"networkID" : "0x1",
+		"chainID": "0x3d",
 		"forkBlock": "0x1d4c00",
 		"forkCanonHash": "0x94365e3a8c0b35089c1d1195081fe7489b528a84b22199c916180db8b28ade7f"
 	},
diff --git a/ethcore/res/ethereum/morden.json b/ethcore/res/ethereum/morden.json
index d21756250..2adea0f8c 100644
--- a/ethcore/res/ethereum/morden.json
+++ b/ethcore/res/ethereum/morden.json
@@ -27,6 +27,7 @@
 		"maximumExtraDataSize": "0x20",
 		"minGasLimit": "0x1388",
 		"networkID" : "0x2",
+		"chainID": "0x3e",
 		"forkBlock": "0x1b34d8",
 		"forkCanonHash": "0xf376243aeff1f256d970714c3de9fd78fa4e63cf63e32a51fe1169e375d98145"
 	},
diff --git a/ethcore/src/ethereum/ethash.rs b/ethcore/src/ethereum/ethash.rs
index feb749e9e..372ac0533 100644
--- a/ethcore/src/ethereum/ethash.rs
+++ b/ethcore/src/ethereum/ethash.rs
@@ -167,7 +167,7 @@ impl Engine for Ethash {
 
 	fn signing_network_id(&self, env_info: &EnvInfo) -> Option<u64> {
 		if env_info.number >= self.ethash_params.eip155_transition {
-			Some(self.params().network_id)
+			Some(self.params().chain_id)
 		} else {
 			None
 		}
@@ -316,7 +316,7 @@ impl Engine for Ethash {
 		}
 
 		if let Some(n) = t.network_id() {
-			if header.number() < self.ethash_params.eip155_transition || n != self.params().network_id {
+			if header.number() < self.ethash_params.eip155_transition || n != self.params().chain_id {
 				return Err(TransactionError::InvalidNetworkId.into())
 			}
 		}
diff --git a/ethcore/src/spec/spec.rs b/ethcore/src/spec/spec.rs
index bdcd5eee2..d3ba52b2e 100644
--- a/ethcore/src/spec/spec.rs
+++ b/ethcore/src/spec/spec.rs
@@ -38,6 +38,8 @@ pub struct CommonParams {
 	pub maximum_extra_data_size: usize,
 	/// Network id.
 	pub network_id: u64,
+	/// Chain id.
+	pub chain_id: u64,
 	/// Main subprotocol name.
 	pub subprotocol_name: String,
 	/// Minimum gas limit.
@@ -52,6 +54,7 @@ impl From<ethjson::spec::Params> for CommonParams {
 			account_start_nonce: p.account_start_nonce.into(),
 			maximum_extra_data_size: p.maximum_extra_data_size.into(),
 			network_id: p.network_id.into(),
+			chain_id: if let Some(n) = p.chain_id { n.into() } else { p.network_id.into() },
 			subprotocol_name: p.subprotocol_name.unwrap_or_else(|| "eth".to_owned()),
 			min_gas_limit: p.min_gas_limit.into(),
 			fork_block: if let (Some(n), Some(h)) = (p.fork_block, p.fork_hash) { Some((n.into(), h.into())) } else { None },
diff --git a/json/src/spec/params.rs b/json/src/spec/params.rs
index 882686319..aeda7d132 100644
--- a/json/src/spec/params.rs
+++ b/json/src/spec/params.rs
@@ -35,6 +35,10 @@ pub struct Params {
 	/// Network id.
 	#[serde(rename="networkID")]
 	pub network_id: Uint,
+	/// Chain id.
+	#[serde(rename="chainID")]
+	pub chain_id: Option<Uint>,
+
 	/// Name of the main ("eth") subprotocol.
 	#[serde(rename="subprotocolName")]
 	pub subprotocol_name: Option<String>,
@@ -58,6 +62,7 @@ mod tests {
 			"homesteadTransition": "0x118c30",
 			"maximumExtraDataSize": "0x20",
 			"networkID" : "0x1",
+			"chainID" : "0x15",
 			"subprotocolName" : "exp",
 			"minGasLimit": "0x1388",
 			"accountStartNonce": "0x00"