diff --git a/wal/wal.go b/wal/wal.go
index 1bc2f2c4e..e63c7d752 100644
--- a/wal/wal.go
+++ b/wal/wal.go
@@ -23,6 +23,7 @@ import (
 	"os"
 	"path"
 	"reflect"
+	"sync"
 	"time"
 
 	"github.com/coreos/etcd/pkg/fileutil"
@@ -69,6 +70,7 @@ type WAL struct {
 	start   walpb.Snapshot // snapshot to start reading
 	decoder *decoder       // decoder to decode records
 
+	mu      sync.Mutex
 	f       *os.File // underlay file opened for appending, sync
 	seq     uint64   // sequence of the wal file currently used for writes
 	enti    uint64   // index of the last entry saved to the wal
@@ -213,6 +215,9 @@ func openAtIndex(dirpath string, snap walpb.Snapshot, all bool) (*WAL, error) {
 // TODO: maybe loose the checking of match.
 // After ReadAll, the WAL will be ready for appending new records.
 func (w *WAL) ReadAll() (metadata []byte, state raftpb.HardState, ents []raftpb.Entry, err error) {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
 	rec := &walpb.Record{}
 	decoder := w.decoder
 
@@ -335,6 +340,9 @@ func (w *WAL) sync() error {
 // For example, if WAL is holding lock 1,2,3,4,5,6, ReleaseLockTo(4) will release
 // lock 1,2 but keep 3. ReleaseLockTo(5) will release 1,2,3 but keep 4.
 func (w *WAL) ReleaseLockTo(index uint64) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
 	var smaller int
 	found := false
 
@@ -370,6 +378,9 @@ func (w *WAL) ReleaseLockTo(index uint64) error {
 }
 
 func (w *WAL) Close() error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
 	if w.f != nil {
 		if err := w.sync(); err != nil {
 			return err
@@ -409,6 +420,9 @@ func (w *WAL) saveState(s *raftpb.HardState) error {
 }
 
 func (w *WAL) Save(st raftpb.HardState, ents []raftpb.Entry) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
 	// short cut, do not call sync
 	if raft.IsEmptyHardState(st) && len(ents) == 0 {
 		return nil
@@ -436,6 +450,9 @@ func (w *WAL) Save(st raftpb.HardState, ents []raftpb.Entry) error {
 }
 
 func (w *WAL) SaveSnapshot(e walpb.Snapshot) error {
+	w.mu.Lock()
+	defer w.mu.Unlock()
+
 	b := pbutil.MustMarshal(&e)
 	rec := &walpb.Record{Type: snapshotType, Data: b}
 	if err := w.encoder.encode(rec); err != nil {