diff --git a/database/single_db.go b/database/single_db.go
index 5e402a5..509039c 100644
--- a/database/single_db.go
+++ b/database/single_db.go
@@ -101,8 +101,7 @@ func (db *DB) Exec(c redis.Connection, cmdLine [][]byte) redis.Reply {
 		return Watch(db, c, cmdLine[1:])
 	}
 	if c != nil && c.InMultiState() {
-		EnqueueCmd(c, cmdLine)
-		return protocol.MakeQueuedReply()
+		return EnqueueCmd(c, cmdLine)
 	}
 
 	return db.execNormalCommand(cmdLine)
diff --git a/database/transaction.go b/database/transaction.go
index ec82437..376de0c 100644
--- a/database/transaction.go
+++ b/database/transaction.go
@@ -51,14 +51,19 @@ func EnqueueCmd(conn redis.Connection, cmdLine [][]byte) redis.Reply {
 	cmdName := strings.ToLower(string(cmdLine[0]))
 	cmd, ok := cmdTable[cmdName]
 	if !ok {
-		return protocol.MakeErrReply("ERR unknown command '" + cmdName + "'")
+		err := protocol.MakeErrReply("ERR unknown command '" + cmdName + "'")
+		conn.AddTxError(err)
+		return err
 	}
 	if cmd.prepare == nil {
-		return protocol.MakeErrReply("ERR command '" + cmdName + "' cannot be used in MULTI")
+		err := protocol.MakeErrReply("ERR command '" + cmdName + "' cannot be used in MULTI")
+		conn.AddTxError(err)
+		return err
 	}
 	if !validateArity(cmd.arity, cmdLine) {
-		// difference with redis: we won't enqueue command line with wrong arity
-		return protocol.MakeArgNumErrReply(cmdName)
+		err := protocol.MakeArgNumErrReply(cmdName)
+		conn.AddTxError(err)
+		return err
 	}
 	conn.EnqueueCmd(cmdLine)
 	return protocol.MakeQueuedReply()
@@ -69,6 +74,9 @@ func execMulti(db *DB, conn redis.Connection) redis.Reply {
 		return protocol.MakeErrReply("ERR EXEC without MULTI")
 	}
 	defer conn.SetMultiState(false)
+	if len(conn.GetTxErrors()) > 0 {
+		return protocol.MakeErrReply("EXECABORT Transaction discarded because of previous errors.")
+	}
 	cmdLines := conn.GetQueuedCmdLine()
 	return db.ExecMulti(conn, conn.GetWatching(), cmdLines)
 }
diff --git a/database/transaction_test.go b/database/transaction_test.go
index e263d2c..bb65527 100644
--- a/database/transaction_test.go
+++ b/database/transaction_test.go
@@ -31,6 +31,20 @@ func TestMulti(t *testing.T) {
 	}
 }
 
+func TestSyntaxErr(t *testing.T) {
+	conn := new(connection.FakeConn)
+	testServer.Exec(conn, utils.ToCmdLine("FLUSHALL"))
+	result := testServer.Exec(conn, utils.ToCmdLine("multi"))
+	asserts.AssertNotError(t, result)
+	result = testServer.Exec(conn, utils.ToCmdLine("set"))
+	asserts.AssertErrReply(t, result, "ERR wrong number of arguments for 'set' command")
+	testServer.Exec(conn, utils.ToCmdLine("get", "a"))
+	result = testServer.Exec(conn, utils.ToCmdLine("exec"))
+	asserts.AssertErrReply(t, result, "EXECABORT Transaction discarded because of previous errors.")
+	result = testServer.Exec(conn, utils.ToCmdLine("get", "a"))
+	asserts.AssertNotError(t, result)
+}
+
 func TestRollback(t *testing.T) {
 	conn := new(connection.FakeConn)
 	testServer.Exec(conn, utils.ToCmdLine("FLUSHALL"))
diff --git a/datastruct/dict/simple.go b/datastruct/dict/simple.go
index 8f24a3c..1ad9402 100644
--- a/datastruct/dict/simple.go
+++ b/datastruct/dict/simple.go
@@ -72,6 +72,7 @@ func (dict *SimpleDict) Keys() []string {
 	i := 0
 	for k := range dict.m {
 		result[i] = k
+		i++
 	}
 	return result
 }
diff --git a/datastruct/dict/simple_test.go b/datastruct/dict/simple_test.go
index 9a52bfd..74f4a4a 100644
--- a/datastruct/dict/simple_test.go
+++ b/datastruct/dict/simple_test.go
@@ -2,18 +2,34 @@ package dict
 
 import (
 	"github.com/hdt3213/godis/lib/utils"
+	"sort"
 	"testing"
 )
 
 func TestSimpleDict_Keys(t *testing.T) {
 	d := MakeSimple()
 	size := 10
+	var expectKeys []string
 	for i := 0; i < size; i++ {
-		d.Put(utils.RandString(5), utils.RandString(5))
+		str := utils.RandString(5)
+		d.Put(str, str)
+		expectKeys = append(expectKeys, str)
 	}
-	if len(d.Keys()) != size {
+	sort.Slice(expectKeys, func(i, j int) bool {
+		return expectKeys[i] > expectKeys[j]
+	})
+	keys := d.Keys()
+	if len(keys) != size {
 		t.Errorf("expect %d keys, actual: %d", size, len(d.Keys()))
 	}
+	sort.Slice(keys, func(i, j int) bool {
+		return keys[i] > keys[j]
+	})
+	for i, k := range keys {
+		if k != expectKeys[i] {
+			t.Errorf("expect %s actual %s", expectKeys[i], k)
+		}
+	}
 }
 
 func TestSimpleDict_PutIfExists(t *testing.T) {
diff --git a/interface/redis/conn.go b/interface/redis/conn.go
index a1b0fc5..05ca534 100644
--- a/interface/redis/conn.go
+++ b/interface/redis/conn.go
@@ -19,6 +19,8 @@ type Connection interface {
 	EnqueueCmd([][]byte)
 	ClearQueuedCmds()
 	GetWatching() map[string]uint32
+	AddTxError(err error)
+	GetTxErrors() []error
 
 	// used for multi database
 	GetDBIndex() int
diff --git a/lib/sync/wait/wait.go b/lib/sync/wait/wait.go
index 1fb99a7..331f5ed 100644
--- a/lib/sync/wait/wait.go
+++ b/lib/sync/wait/wait.go
@@ -31,7 +31,7 @@ func (w *Wait) WaitWithTimeout(timeout time.Duration) bool {
 	c := make(chan bool, 1)
 	go func() {
 		defer close(c)
-		w.wg.Wait()
+		w.Wait()
 		c <- true
 	}()
 	select {
diff --git a/redis/connection/conn.go b/redis/connection/conn.go
index 6aab461..67d5a0b 100644
--- a/redis/connection/conn.go
+++ b/redis/connection/conn.go
@@ -35,6 +35,7 @@ type Connection struct {
 	multiState bool
 	queue      [][][]byte
 	watching   map[string]uint32
+	txErrors   []error
 
 	// selected db
 	selectedDB int
@@ -65,11 +66,9 @@ func (c *Connection) Write(b []byte) error {
 	if len(b) == 0 {
 		return nil
 	}
-	c.mu.Lock()
 	c.waitingReply.Add(1)
 	defer func() {
 		c.waitingReply.Done()
-		c.mu.Unlock()
 	}()
 
 	_, err := c.conn.Write(b)
@@ -151,6 +150,16 @@ func (c *Connection) EnqueueCmd(cmdLine [][]byte) {
 	c.queue = append(c.queue, cmdLine)
 }
 
+// AddTxError stores syntax error within transaction
+func (c *Connection) AddTxError(err error) {
+	c.txErrors = append(c.txErrors, err)
+}
+
+// GetTxErrors returns syntax error within transaction
+func (c *Connection) GetTxErrors() []error {
+	return c.txErrors
+}
+
 // ClearQueuedCmds clears queued commands of current transaction
 func (c *Connection) ClearQueuedCmds() {
 	c.queue = nil