diff --git a/core/src/client/client.rs b/core/src/client/client.rs
index c5dbf07bdb..f99e76098f 100644
--- a/core/src/client/client.rs
+++ b/core/src/client/client.rs
@@ -481,6 +481,10 @@ impl StateInfo for Client {
 }
 
 impl EngineInfo for Client {
+    fn network_id(&self) -> NetworkId {
+        self.common_params(BlockId::Earliest).expect("Genesis state must exist").network_id()
+    }
+
     fn common_params(&self, block_id: BlockId) -> Option<CommonParams> {
         self.state_info(block_id.into()).map(|state| {
             state
@@ -518,7 +522,7 @@ impl EngineInfo for Client {
     }
 
     fn possible_authors(&self, block_number: Option<u64>) -> Result<Option<Vec<PlatformAddress>>, EngineError> {
-        let network_id = self.common_params(BlockId::Latest).unwrap().network_id();
+        let network_id = self.network_id();
         if block_number == Some(0) {
             let genesis_author = self.block_header(&0.into()).expect("genesis block").author();
             return Ok(Some(vec![PlatformAddress::new_v1(network_id, genesis_author)]))
@@ -572,8 +576,7 @@ impl BlockChainTrait for Client {
     }
 
     fn genesis_accounts(&self) -> Vec<PlatformAddress> {
-        // XXX: What should we do if the network id has been changed
-        let network_id = self.common_params(BlockId::Latest).unwrap().network_id();
+        let network_id = self.network_id();
         self.genesis_accounts.iter().map(|addr| PlatformAddress::new_v1(network_id, *addr)).collect()
     }
 
@@ -887,10 +890,6 @@ impl MiningBlockChainClient for Client {
     fn register_immune_users(&self, immune_user_vec: Vec<Address>) {
         self.importer.miner.register_immune_users(immune_user_vec)
     }
-
-    fn get_network_id(&self) -> NetworkId {
-        self.common_params(BlockId::Latest).unwrap().network_id()
-    }
 }
 
 impl ChainTimeInfo for Client {
diff --git a/core/src/client/mod.rs b/core/src/client/mod.rs
index dd42b863d1..f331bb90e3 100644
--- a/core/src/client/mod.rs
+++ b/core/src/client/mod.rs
@@ -87,6 +87,7 @@ pub trait BlockChainTrait {
 }
 
 pub trait EngineInfo: Send + Sync {
+    fn network_id(&self) -> NetworkId;
     fn common_params(&self, block_id: BlockId) -> Option<CommonParams>;
     fn metadata_seq(&self, block_id: BlockId) -> Option<u64>;
     fn block_reward(&self, block_number: u64) -> u64;
@@ -279,9 +280,6 @@ pub trait MiningBlockChainClient: BlockChainClient + BlockProducer + FindActionH
 
     /// Append designated users to the immune user list.
     fn register_immune_users(&self, immune_user_vec: Vec<Address>);
-
-    /// Returns network id.
-    fn get_network_id(&self) -> NetworkId;
 }
 
 /// Provides methods to access database.
diff --git a/core/src/client/test_client.rs b/core/src/client/test_client.rs
index f8b0252119..0ef27d3b19 100644
--- a/core/src/client/test_client.rs
+++ b/core/src/client/test_client.rs
@@ -380,10 +380,6 @@ impl MiningBlockChainClient for TestBlockChainClient {
     fn register_immune_users(&self, immune_user_vec: Vec<Address>) {
         self.miner.register_immune_users(immune_user_vec)
     }
-
-    fn get_network_id(&self) -> NetworkId {
-        NetworkId::default()
-    }
 }
 
 impl AccountData for TestBlockChainClient {
@@ -632,6 +628,10 @@ impl super::EngineClient for TestBlockChainClient {
 }
 
 impl EngineInfo for TestBlockChainClient {
+    fn network_id(&self) -> NetworkId {
+        self.scheme.engine.machine().genesis_common_params().network_id()
+    }
+
     fn common_params(&self, _block_id: BlockId) -> Option<CommonParams> {
         Some(*self.scheme.engine.machine().genesis_common_params())
     }
diff --git a/core/src/consensus/stake/action_data.rs b/core/src/consensus/stake/action_data.rs
index 7c59dc9135..34bc90ab72 100644
--- a/core/src/consensus/stake/action_data.rs
+++ b/core/src/consensus/stake/action_data.rs
@@ -433,6 +433,10 @@ impl CurrentValidators {
     pub fn update(&mut self, validators: Vec<Validator>) {
         self.0 = validators;
     }
+
+    pub fn addresses(&self) -> Vec<Address> {
+        self.0.iter().rev().map(|v| public_to_address(&v.pubkey)).collect()
+    }
 }
 
 impl Deref for CurrentValidators {
diff --git a/core/src/consensus/tendermint/engine.rs b/core/src/consensus/tendermint/engine.rs
index 67a83dc4d1..24b10b70a3 100644
--- a/core/src/consensus/tendermint/engine.rs
+++ b/core/src/consensus/tendermint/engine.rs
@@ -160,7 +160,7 @@ impl ConsensusEngine for Tendermint {
 
         if block_number == metadata.last_term_finished_block_num() + 1 {
             match term {
-                0 => {}
+                0 | 1 => {}
                 _ => {
                     let rewards = stake::drain_current_rewards(block.state_mut())?;
                     let banned = stake::Banned::load_from_state(block.state())?;
@@ -389,20 +389,24 @@ fn aggregate_work_info(
         end_of_the_last_term + 1
     };
     let mut header = start_of_the_next_term_header;
-    let mut parent_validators = validators.current_addresses(&header.parent_hash());
+    // FIXME: Use method from `ValidatorSet` interface
+    let mut current_validators = {
+        let state = chain.state_at(header.parent_hash().into()).expect("The block's state must exist");
+        stake::CurrentValidators::load_from_state(&state)?.addresses()
+    };
     while start_of_the_current_term != header.number() {
         for index in TendermintSealView::new(&header.seal()).bitset()?.true_index_iter() {
-            let signer = *parent_validators.get(index).expect("The seal must be the signature of the validator");
+            let signer = *current_validators.get(index).expect("The seal must be the signature of the validator");
             work_info.entry(signer).or_default().signed += 1;
         }
 
         header = chain.block_header(&header.parent_hash().into()).unwrap();
-        parent_validators = validators.current_addresses(&header.parent_hash());
+        current_validators = validators.current_addresses(&header.parent_hash());
 
         let author = header.author();
         let info = work_info.entry(author).or_default();
         info.proposed += 1;
-        info.missed += parent_validators.len() - TendermintSealView::new(&header.seal()).bitset()?.count();
+        info.missed += current_validators.len() - TendermintSealView::new(&header.seal()).bitset()?.count();
     }
 
     Ok(work_info)
diff --git a/core/src/consensus/tendermint/worker.rs b/core/src/consensus/tendermint/worker.rs
index 5956ad6d9a..75e7d65294 100644
--- a/core/src/consensus/tendermint/worker.rs
+++ b/core/src/consensus/tendermint/worker.rs
@@ -1219,13 +1219,14 @@ impl Worker {
         };
 
         let mut voted_validators = BitSet::new();
-        let grand_parent_hash = self
-            .client()
-            .block_header(&(*header.parent_hash()).into())
-            .expect("The parent block must exist")
-            .parent_hash();
+        let parent_hash = header.parent_hash();
+        let grand_parent_hash =
+            self.client().block_header(&(*parent_hash).into()).expect("The parent block must exist").parent_hash();
         for (bitset_index, signature) in seal_view.signatures()? {
-            let public = self.validators.get(&grand_parent_hash, bitset_index);
+            let public = match self.validators.get_current(header.parent_hash(), bitset_index) {
+                Some(p) => p,
+                None => self.validators.get(&grand_parent_hash, bitset_index),
+            };
             if !verify_schnorr(&public, &signature, &precommit_vote_on.hash())? {
                 let address = public_to_address(&public);
                 return Err(EngineError::BlockNotAuthorized(address.to_owned()).into())
@@ -1238,7 +1239,7 @@ impl Worker {
         if header.number() == 1 {
             return Ok(())
         }
-        self.validators.check_enough_votes(&grand_parent_hash, &voted_validators)?;
+        self.validators.check_enough_votes_with_current(&parent_hash, &voted_validators)?;
         Ok(())
     }
 
@@ -1446,7 +1447,7 @@ impl Worker {
     }
 
     fn report_double_vote(&self, double: &DoubleVote) {
-        let network_id = self.client().common_params(BlockId::Latest).unwrap().network_id();
+        let network_id = self.client().network_id();
         let seq = match self.signer.address() {
             Some(address) => self.client().latest_seq(address),
             None => {
diff --git a/core/src/consensus/validator_set/dynamic_validator.rs b/core/src/consensus/validator_set/dynamic_validator.rs
index 19fa775db8..63ae1ffdd5 100644
--- a/core/src/consensus/validator_set/dynamic_validator.rs
+++ b/core/src/consensus/validator_set/dynamic_validator.rs
@@ -104,6 +104,44 @@ impl DynamicValidator {
             (prev_proposer_index + proposed_view + 1) % num_validators
         }
     }
+
+    pub fn get_current(&self, hash: &BlockHash, index: usize) -> Option<Public> {
+        let validators = self.current_validators_pubkey(*hash)?;
+        let n_validators = validators.len();
+        Some(*validators.get(index % n_validators).unwrap())
+    }
+
+    pub fn check_enough_votes_with_current(&self, hash: &BlockHash, votes: &BitSet) -> Result<(), EngineError> {
+        if let Some(validators) = self.current_validators(*hash) {
+            let mut voted_delegation = 0u64;
+            let n_validators = validators.len();
+            for index in votes.true_index_iter() {
+                assert!(index < n_validators);
+                let validator = validators.get(index).ok_or_else(|| {
+                    EngineError::ValidatorNotExist {
+                        height: 0, // FIXME
+                        index,
+                    }
+                })?;
+                voted_delegation += validator.delegation();
+            }
+            let total_delegation: u64 = validators.iter().map(Validator::delegation).sum();
+            if voted_delegation * 3 > total_delegation * 2 {
+                Ok(())
+            } else {
+                let threshold = total_delegation as usize * 2 / 3;
+                Err(EngineError::BadSealFieldSize(OutOfBounds {
+                    min: Some(threshold),
+                    max: Some(total_delegation as usize),
+                    found: voted_delegation as usize,
+                }))
+            }
+        } else {
+            let client = self.client.read().as_ref().and_then(Weak::upgrade).expect("Client is not initialized");
+            let header = client.block_header(&(*hash).into()).unwrap();
+            self.check_enough_votes(&header.parent_hash(), votes)
+        }
+    }
 }
 
 impl ValidatorSet for DynamicValidator {
diff --git a/foundry/run_node.rs b/foundry/run_node.rs
index 2fa44e59ba..51c0782513 100644
--- a/foundry/run_node.rs
+++ b/foundry/run_node.rs
@@ -262,7 +262,7 @@ pub fn run_node(matches: &ArgMatches<'_>) -> Result<(), String> {
             let network_config = config.network_config()?;
             // XXX: What should we do if the network id has been changed.
             let c = client.client();
-            let network_id = c.common_params(BlockId::Latest).unwrap().network_id();
+            let network_id = c.network_id();
             let routing_table = RoutingTable::new();
             let service = network_start(network_id, timer_loop, &network_config, Arc::clone(&routing_table))?;
 
diff --git a/rpc/src/v1/impls/account.rs b/rpc/src/v1/impls/account.rs
index a4c16207e9..fa10fbc063 100644
--- a/rpc/src/v1/impls/account.rs
+++ b/rpc/src/v1/impls/account.rs
@@ -18,8 +18,8 @@ use std::convert::TryInto;
 use std::sync::Arc;
 use std::time::Duration;
 
-use ccore::{AccountData, AccountProvider, BlockId, EngineInfo, MinerService, MiningBlockChainClient, TermInfo};
-use ckey::{NetworkId, Password, PlatformAddress, Signature};
+use ccore::{AccountData, AccountProvider, EngineInfo, MinerService, MiningBlockChainClient, TermInfo};
+use ckey::{Password, PlatformAddress, Signature};
 use ctypes::transaction::IncompleteTransaction;
 use jsonrpc_core::Result;
 use parking_lot::Mutex;
@@ -46,11 +46,6 @@ where
             miner,
         }
     }
-
-    fn network_id(&self) -> NetworkId {
-        // XXX: What should we do if the network id has been changed
-        self.client.common_params(BlockId::Latest).unwrap().network_id()
-    }
 }
 
 impl<C, M> Account for AccountClient<C, M>
@@ -62,7 +57,10 @@ where
         self.account_provider
             .get_list()
             .map(|addresses| {
-                addresses.into_iter().map(|address| PlatformAddress::new_v1(self.network_id(), address)).collect()
+                addresses
+                    .into_iter()
+                    .map(|address| PlatformAddress::new_v1(self.client.network_id(), address))
+                    .collect()
             })
             .map_err(account_provider)
     }
@@ -70,13 +68,13 @@ where
     fn create_account(&self, passphrase: Option<Password>) -> Result<PlatformAddress> {
         let (address, _) =
             self.account_provider.new_account_and_public(&passphrase.unwrap_or_default()).map_err(account_provider)?;
-        Ok(PlatformAddress::new_v1(self.network_id(), address))
+        Ok(PlatformAddress::new_v1(self.client.network_id(), address))
     }
 
     fn create_account_from_secret(&self, secret: H256, passphrase: Option<Password>) -> Result<PlatformAddress> {
         self.account_provider
             .insert_account(secret.into(), &passphrase.unwrap_or_default())
-            .map(|address| PlatformAddress::new_v1(self.network_id(), address))
+            .map(|address| PlatformAddress::new_v1(self.client.network_id(), address))
             .map_err(account_provider)
     }
 
diff --git a/rpc/src/v1/impls/chain.rs b/rpc/src/v1/impls/chain.rs
index 576e571d00..d9a3797f0c 100644
--- a/rpc/src/v1/impls/chain.rs
+++ b/rpc/src/v1/impls/chain.rs
@@ -128,10 +128,11 @@ where
             return Ok(None)
         }
         let block_id = block_number.map(BlockId::from).unwrap_or(BlockId::Latest);
-        Ok(self.client.get_text(transaction_hash, block_id).map_err(errors::transaction_state)?.map(|text| {
-            let parent_block_id = block_number.map(|n| (n - 1).into()).unwrap_or(BlockId::ParentOfLatest);
-            Text::from_core(text, self.client.common_params(parent_block_id).unwrap().network_id())
-        }))
+        Ok(self
+            .client
+            .get_text(transaction_hash, block_id)
+            .map_err(errors::transaction_state)?
+            .map(|text| Text::from_core(text, self.client.network_id())))
     }
 
     fn get_asset(
@@ -178,8 +179,7 @@ where
     fn get_regular_key_owner(&self, public: Public, block_number: Option<u64>) -> Result<Option<PlatformAddress>> {
         let block_id = block_number.map(BlockId::Number).unwrap_or(BlockId::Latest);
         Ok(self.client.regular_key_owner(&public_to_address(&public), block_id.into()).and_then(|address| {
-            let parent_block_id = block_number.map(|n| (n - 1).into()).unwrap_or(BlockId::ParentOfLatest);
-            let network_id = self.client.common_params(parent_block_id).unwrap().network_id();
+            let network_id = self.client.network_id();
             Some(PlatformAddress::new_v1(network_id, address))
         }))
     }
@@ -206,8 +206,7 @@ where
     fn get_shard_owners(&self, shard_id: ShardId, block_number: Option<u64>) -> Result<Option<Vec<PlatformAddress>>> {
         let block_id = block_number.map(BlockId::Number).unwrap_or(BlockId::Latest);
         Ok(self.client.shard_owners(shard_id, block_id.into()).map(|owners| {
-            let parent_block_id = block_number.map(|n| (n - 1).into()).unwrap_or(BlockId::ParentOfLatest);
-            let network_id = self.client.common_params(parent_block_id).unwrap().network_id();
+            let network_id = self.client.network_id();
             owners.into_iter().map(|owner| PlatformAddress::new_v1(network_id, owner)).collect()
         }))
     }
@@ -215,8 +214,7 @@ where
     fn get_shard_users(&self, shard_id: ShardId, block_number: Option<u64>) -> Result<Option<Vec<PlatformAddress>>> {
         let block_id = block_number.map(BlockId::Number).unwrap_or(BlockId::Latest);
         Ok(self.client.shard_users(shard_id, block_id.into()).map(|users| {
-            let parent_block_id = block_number.map(|n| (n - 1).into()).unwrap_or(BlockId::ParentOfLatest);
-            let network_id = self.client.common_params(parent_block_id).unwrap().network_id();
+            let network_id = self.client.network_id();
             users.into_iter().map(|user| PlatformAddress::new_v1(network_id, user)).collect()
         }))
     }
@@ -239,26 +237,14 @@ where
 
     fn get_block_by_number(&self, block_number: u64) -> Result<Option<Block>> {
         let id = BlockId::Number(block_number);
-        Ok(self.client.block(&id).map(|block| {
-            let block_id_to_read_params = if block_number == 0 {
-                0.into()
-            } else {
-                (block_number - 1).into()
-            };
-            Block::from_core(block.decode(), self.client.common_params(block_id_to_read_params).unwrap().network_id())
-        }))
+        Ok(self.client.block(&id).map(|block| Block::from_core(block.decode(), self.client.network_id())))
     }
 
     fn get_block_by_hash(&self, block_hash: BlockHash) -> Result<Option<Block>> {
         let id = BlockId::Hash(block_hash);
         Ok(self.client.block(&id).map(|block| {
             let block = block.decode();
-            let block_id_to_read_params = if block.header.number() == 0 {
-                0.into()
-            } else {
-                (*block.header.parent_hash()).into()
-            };
-            Block::from_core(block, self.client.common_params(block_id_to_read_params).unwrap().network_id())
+            Block::from_core(block, self.client.network_id())
         }))
     }
 
@@ -301,7 +287,7 @@ where
     }
 
     fn get_network_id(&self) -> Result<NetworkId> {
-        Ok(self.client.common_params(BlockId::Latest).unwrap().network_id())
+        Ok(self.client.network_id())
     }
 
     fn get_common_params(&self, block_number: Option<u64>) -> Result<Option<Params>> {
diff --git a/rpc/src/v1/impls/engine.rs b/rpc/src/v1/impls/engine.rs
index f106f29346..730ec09073 100644
--- a/rpc/src/v1/impls/engine.rs
+++ b/rpc/src/v1/impls/engine.rs
@@ -62,7 +62,7 @@ where
             Ok(None)
         } else {
             // XXX: What should we do if the network id has been changed
-            let network_id = self.client.common_params(BlockId::Latest).unwrap().network_id();
+            let network_id = self.client.network_id();
             Ok(Some(PlatformAddress::new_v1(network_id, author)))
         }
     }
diff --git a/rpc/src/v1/impls/mempool.rs b/rpc/src/v1/impls/mempool.rs
index ed021f1c8d..ab78c740e8 100644
--- a/rpc/src/v1/impls/mempool.rs
+++ b/rpc/src/v1/impls/mempool.rs
@@ -16,7 +16,7 @@
 
 use std::sync::Arc;
 
-use ccore::{BlockChainClient, MiningBlockChainClient, SignedTransaction};
+use ccore::{BlockChainClient, EngineInfo, MiningBlockChainClient, SignedTransaction};
 use cjson::bytes::Bytes;
 use ckey::{Address, PlatformAddress};
 use ctypes::{Tracker, TxHash};
@@ -42,7 +42,7 @@ impl<C> MempoolClient<C> {
 
 impl<C> Mempool for MempoolClient<C>
 where
-    C: BlockChainClient + MiningBlockChainClient + 'static,
+    C: BlockChainClient + MiningBlockChainClient + EngineInfo + 'static,
 {
     fn send_signed_transaction(&self, raw: Bytes) -> Result<TxHash> {
         Rlp::new(&raw.into_vec())
@@ -82,7 +82,7 @@ where
 
     fn get_banned_accounts(&self) -> Result<Vec<PlatformAddress>> {
         let malicious_user_vec = self.client.get_malicious_users();
-        let network_id = self.client.get_network_id();
+        let network_id = self.client.network_id();
         Ok(malicious_user_vec.into_iter().map(|address| PlatformAddress::new_v1(network_id, address)).collect())
     }
 
@@ -102,7 +102,7 @@ where
 
     fn get_immune_accounts(&self) -> Result<Vec<PlatformAddress>> {
         let immune_user_vec = self.client.get_immune_users();
-        let network_id = self.client.get_network_id();
+        let network_id = self.client.network_id();
         Ok(immune_user_vec.into_iter().map(|address| PlatformAddress::new_v1(network_id, address)).collect())
     }