diff --git a/blockproducer/chain.go b/blockproducer/chain.go
index b07768e23..ac737d573 100644
--- a/blockproducer/chain.go
+++ b/blockproducer/chain.go
@@ -311,7 +311,6 @@ func (c *Chain) produceBlock(now time.Time) (err error) {
 
 	for _, s := range c.getPeers().Servers {
 		if !s.IsEqual(&c.nodeID) {
-			// Bind NodeID to subroutine
 			func(id proto.NodeID) {
 				c.goFuncWithTimeout(func(ctx context.Context) {
 					var (
@@ -336,7 +335,6 @@ func (c *Chain) produceBlock(now time.Time) (err error) {
 			}(s)
 		}
 	}
-
 	return err
 }
 
@@ -471,10 +469,31 @@ func (c *Chain) processBlocks(ctx context.Context) {
 }
 
 func (c *Chain) addTx(tx pi.Transaction) {
-	// Simple non-blocking broadcasting
-	for _, v := range c.getPeers().Servers {
-		if !v.IsEqual(&c.nodeID) {
-			// Bind NodeID to subroutine
+	select {
+	case c.pendingTxs <- tx:
+	case <-c.ctx.Done():
+		log.WithError(c.ctx.Err()).Warn("add transaction aborted")
+	}
+}
+
+func (c *Chain) processTx(tx pi.Transaction) {
+	if err := tx.Verify(); err != nil {
+		log.WithError(err).Errorf("failed to verify transaction with hash: %s, address: %s, tx type: %s", tx.Hash(), tx.GetAccountAddress(), tx.GetTransactionType().String())
+		return
+	}
+	if ok := func() (ok bool) {
+		c.RLock()
+		defer c.RUnlock()
+		_, ok = c.txPool[tx.Hash()]
+		return
+	}(); ok {
+		log.WithFields(log.Fields{
+			"tx_hash": tx.Hash().Short(4),
+		}).Debug("tx already exists, abort processing")
+		return
+	}
+	for _, s := range c.getPeers().Servers {
+		if !s.IsEqual(&c.nodeID) {
 			func(id proto.NodeID) {
 				c.goFuncWithTimeout(func(ctx context.Context) {
 					var (
@@ -494,23 +513,10 @@ func (c *Chain) addTx(tx pi.Transaction) {
 						"tx_hash": tx.Hash().Short(4),
 						"tx_type": tx.GetTransactionType(),
 					}).WithError(err).Debug("broadcasting transaction to other peers")
-				}, c.period)
-			}(v)
+				}, c.tick)
+			}(s)
 		}
 	}
-
-	select {
-	case c.pendingTxs <- tx:
-	case <-c.ctx.Done():
-		log.WithError(c.ctx.Err()).Warn("add transaction aborted")
-	}
-}
-
-func (c *Chain) processTx(tx pi.Transaction) {
-	if err := tx.Verify(); err != nil {
-		log.WithError(err).Error("failed to verify transaction")
-		return
-	}
 	if err := c.storeTx(tx); err != nil {
 		log.WithError(err).Error("failed to add transaction")
 	}
@@ -562,25 +568,22 @@ func (c *Chain) mainCycle(ctx context.Context) {
 }
 
 func (c *Chain) syncCurrentHead(ctx context.Context) {
+	var h = c.getNextHeight() - 1
+	if c.head().height >= h {
+		return
+	}
+	// Initiate blocking gossip calls to fetch block of the current height,
+	// with timeout of one tick.
 	var (
-		h        = c.getNextHeight() - 1
-		cld, ccl = context.WithTimeout(ctx, c.tick)
 		wg       = &sync.WaitGroup{}
+		cld, ccl = context.WithTimeout(ctx, c.tick)
 	)
-
 	defer func() {
 		wg.Wait()
 		ccl()
 	}()
-
-	if c.head().height >= h {
-		return
-	}
-
-	// Initiate blocking gossip calls to fetch block of the current height,
-	// with timeout of one tick.
-	for _, v := range c.getPeers().Servers {
-		if !v.IsEqual(&c.nodeID) {
+	for _, s := range c.getPeers().Servers {
+		if !s.IsEqual(&c.nodeID) {
 			wg.Add(1)
 			go func(id proto.NodeID) {
 				defer wg.Done()
@@ -616,7 +619,7 @@ func (c *Chain) syncCurrentHead(ctx context.Context) {
 				case <-cld.Done():
 					log.WithError(cld.Err()).Warn("add pending block aborted")
 				}
-			}(v)
+			}(s)
 		}
 	}
 }
@@ -763,7 +766,7 @@ func (c *Chain) replaceAndSwitchToBranch(
 						}
 						return fmt.Sprintf("[%04d]", i)
 					}(),
-				}).Debugf("pruning branch")
+				}).Debug("pruning branch")
 			}
 		}
 		// Replace current branches
@@ -990,8 +993,8 @@ func (c *Chain) goFuncWithTimeout(f func(ctx context.Context), timeout time.Dura
 	go func() {
 		var ctx, ccl = context.WithTimeout(c.ctx, timeout)
 		defer func() {
-			ccl()
 			c.wg.Done()
+			ccl()
 		}()
 		f(ctx)
 	}()
diff --git a/crypto/verifier/common.go b/crypto/verifier/common.go
index 41fa8ecb4..7885eb67a 100644
--- a/crypto/verifier/common.go
+++ b/crypto/verifier/common.go
@@ -75,7 +75,7 @@ func (i *DefaultHashSignVerifierImpl) Verify(mh MarshalHasher) (err error) {
 		err = errors.WithStack(ErrHashValueNotMatch)
 		return
 	}
-	if !i.Signature.Verify(h[:], i.Signee) {
+	if i.Signature == nil || i.Signee == nil || !i.Signature.Verify(h[:], i.Signee) {
 		err = errors.WithStack(ErrSignatureNotMatch)
 		return
 	}
diff --git a/crypto/verifier/common_test.go b/crypto/verifier/common_test.go
index 953ce61f8..c9ab5fd84 100644
--- a/crypto/verifier/common_test.go
+++ b/crypto/verifier/common_test.go
@@ -79,6 +79,20 @@ func TestDefaultHashSignVerifierImpl(t *testing.T) {
 					So(err, ShouldEqual, ErrHashValueNotMatch)
 				})
 			})
+			Convey("When the signee is not set", func() {
+				obj.HSV.Signee = nil
+				Convey("The verifier should return signature not match error", func() {
+					err = errors.Cause(obj.Verify())
+					So(err, ShouldEqual, ErrSignatureNotMatch)
+				})
+			})
+			Convey("When the signature is not set", func() {
+				obj.HSV.Signature = nil
+				Convey("The verifier should return signature not match error", func() {
+					err = errors.Cause(obj.Verify())
+					So(err, ShouldEqual, ErrSignatureNotMatch)
+				})
+			})
 			Convey("When the signee is modified", func() {
 				var _, pub, err = asymmetric.GenSecp256k1KeyPair()
 				So(err, ShouldBeNil)