diff --git a/wal/wal.go b/wal/wal.go
index 73c95e906..ff8e79649 100644
--- a/wal/wal.go
+++ b/wal/wal.go
@@ -330,27 +330,34 @@ func (w *WAL) sync() error {
 	return err
 }
 
-// ReleaseLockTo releases the locks w is holding, which
-// have index smaller or equal to the given index.
+// ReleaseLockTo releases the locks, which has smaller index than the given index
+// except the largest one among them.
+// 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 {
-	for _, l := range w.locks {
-		_, i, err := parseWalName(path.Base(l.Name()))
+	var smaller int
+
+	for i, l := range w.locks {
+		_, lockIndex, err := parseWalName(path.Base(l.Name()))
 		if err != nil {
 			return err
 		}
-		if i > index {
-			return nil
+		if lockIndex >= index {
+			smaller = i - 1
+			break
 		}
-		err = l.Unlock()
-		if err != nil {
-			return err
-		}
-		err = l.Destroy()
-		if err != nil {
-			return err
-		}
-		w.locks = w.locks[1:]
 	}
+
+	if smaller <= 0 {
+		return nil
+	}
+
+	for i := 0; i < smaller; i++ {
+		w.locks[i].Unlock()
+		w.locks[i].Destroy()
+	}
+	w.locks = w.locks[smaller:]
+
 	return nil
 }
 
diff --git a/wal/wal_test.go b/wal/wal_test.go
index 76d7c5414..33b727573 100644
--- a/wal/wal_test.go
+++ b/wal/wal_test.go
@@ -435,6 +435,7 @@ func TestOpenNotInUse(t *testing.T) {
 	unlockIndex := uint64(5)
 	w.ReleaseLockTo(unlockIndex)
 
+	// 1,2,3 are avaliable.
 	w2, err := OpenNotInUse(p, walpb.Snapshot{})
 	defer w2.Close()
 	if err != nil {
@@ -444,8 +445,8 @@ func TestOpenNotInUse(t *testing.T) {
 	if err != nil {
 		t.Fatalf("err = %v, want nil", err)
 	}
-	if g := ents[len(ents)-1].Index; g != unlockIndex {
-		t.Errorf("last index read = %d, want %d", g, unlockIndex)
+	if g := ents[len(ents)-1].Index; g != unlockIndex-2 {
+		t.Errorf("last index read = %d, want %d", g, unlockIndex-2)
 	}
 }
 
@@ -462,3 +463,45 @@ func TestSaveEmpty(t *testing.T) {
 		t.Errorf("buf.Bytes = %d, want 0", len(buf.Bytes()))
 	}
 }
+
+func TestReleaseLockTo(t *testing.T) {
+	p, err := ioutil.TempDir(os.TempDir(), "waltest")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(p)
+	// create WAL
+	w, err := Create(p, nil)
+	defer w.Close()
+	if err != nil {
+		t.Fatal(err)
+	}
+	// make 10 seperate files
+	for i := 0; i < 10; i++ {
+		es := []raftpb.Entry{{Index: uint64(i)}}
+		if err = w.Save(raftpb.HardState{}, es); err != nil {
+			t.Fatal(err)
+		}
+		if err = w.cut(); err != nil {
+			t.Fatal(err)
+		}
+	}
+	// release the lock to 5
+	unlockIndex := uint64(5)
+	w.ReleaseLockTo(unlockIndex)
+
+	// expected remaining are 4,5,6,7,8,9,10
+	if len(w.locks) != 7 {
+		t.Errorf("len(w.locks) = %d, want %d", len(w.locks), 7)
+	}
+	for i, l := range w.locks {
+		_, lockIndex, err := parseWalName(path.Base(l.Name()))
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if lockIndex != uint64(i+4) {
+			t.Errorf("#%d: lockindex = %d, want %d", i, lockIndex, uint64(i+4))
+		}
+	}
+}