diff --git a/dir.go b/dir.go
index c3f1936..9aaffec 100644
--- a/dir.go
+++ b/dir.go
@@ -26,6 +26,7 @@ import (
 	"errors"
 	"os"
 	"path"
+	"sync"
 
 	"bazil.org/fuse"
 	"bazil.org/fuse/fs"
@@ -42,22 +43,23 @@ type verDir struct {
 	node   *verNode
 	inode  uint64
 	parent *verDir
+	mutex  sync.Mutex
 }
 
 func newVerDir(node *verNode, parent *verDir) *verDir {
 	dirs := make(map[string]*verDir)
 	files := make(map[string]*verFile)
+	mutex := sync.Mutex{}
 
-	return &verDir{dirs, files, node, allocInode(), parent}
+	return &verDir{dirs, files, node, allocInode(), parent, mutex}
 }
 
 func (vd *verDir) version() error {
-	if vd.node.flags&NodeFlagVer == NodeFlagVer {
+	if vd.node.flags&NodeFlagNew == NodeFlagNew {
 		return nil
 	}
 
-	node := newVerNode(vd.node.path, vd.node.ver.db.lastVersion(), vd.node, NodeFlagDir|NodeFlagVer)
-
+	node := newVerNode(vd.node.path, vd.node.ver.db.lastVersion(), vd.node, NodeFlagDir|NodeFlagNew)
 	if err := os.MkdirAll(node.rebasedPath(), 0755); err != nil {
 		return err
 	}
@@ -78,7 +80,7 @@ func (vd *verDir) createDir(name string) (*verDir, error) {
 		return nil, err
 	}
 
-	node := newVerNode(childPath, vd.node.ver, nil, NodeFlagDir|NodeFlagVer)
+	node := newVerNode(childPath, vd.node.ver, nil, NodeFlagDir|NodeFlagNew)
 	dir := newVerDir(node, vd)
 	vd.dirs[name] = dir
 	node.ver.meta.createNode(node.path)
@@ -86,24 +88,24 @@ func (vd *verDir) createDir(name string) (*verDir, error) {
 	return dir, nil
 }
 
-func (vd *verDir) createFile(name string, flags fuse.OpenFlags, mode os.FileMode) (*verFile, *verFileHandle, error) {
+func (vd *verDir) createFile(name string, flags fuse.OpenFlags, mode os.FileMode) (*verFile, *verFileHandle, fuse.HandleID, error) {
 	if err := vd.version(); err != nil {
-		return nil, nil, err
+		return nil, nil, 0, err
 	}
 
 	childPath := path.Join(vd.node.path, name)
-	node := newVerNode(childPath, vd.node.ver, nil, NodeFlagVer)
+	node := newVerNode(childPath, vd.node.ver, nil, NodeFlagNew)
 	file := newVerFile(node, vd)
 
-	handle, err := file.open(flags, mode)
+	handle, id, err := file.open(flags, mode)
 	if err != nil {
-		return nil, nil, err
+		return nil, nil, 0, err
 	}
 
 	vd.files[name] = file
 	node.ver.meta.createNode(node.path)
 
-	return file, handle, nil
+	return file, handle, id, nil
 }
 
 // Node
@@ -129,11 +131,14 @@ func (vd *verDir) Setattr(ctx context.Context, req *fuse.SetattrRequest, resp *f
 
 // NodeCreater
 func (vd *verDir) Create(ctx context.Context, req *fuse.CreateRequest, resp *fuse.CreateResponse) (node fs.Node, handle fs.Handle, err error) {
+	vd.mutex.Lock()
+	defer vd.mutex.Unlock()
+
 	if req.Mode.IsDir() {
 		node, err = vd.createDir(req.Name)
 		handle = node
 	} else if req.Mode.IsRegular() {
-		node, handle, err = vd.createFile(req.Name, req.Flags, req.Mode)
+		node, handle, resp.Handle, err = vd.createFile(req.Name, req.Flags, req.Mode)
 	} else {
 		err = errors.New("unsupported filetype")
 	}
@@ -143,16 +148,22 @@ func (vd *verDir) Create(ctx context.Context, req *fuse.CreateRequest, resp *fus
 
 // NodeMkdirer
 func (vd *verDir) Mkdir(ctx context.Context, req *fuse.MkdirRequest) (fs.Node, error) {
+	vd.mutex.Lock()
+	defer vd.mutex.Unlock()
+
 	return vd.createDir(req.Name)
 }
 
 // NodeRemover
 func (vd *verDir) Remove(ctx context.Context, req *fuse.RemoveRequest) error {
+	vd.mutex.Lock()
+	defer vd.mutex.Unlock()
+
 	if req.Dir {
 		node := vd.dirs[req.Name].node
 		ver := node.ver
 
-		if node.flags&NodeFlagVer == NodeFlagVer {
+		if node.flags&NodeFlagNew == NodeFlagNew {
 			if err := os.Remove(node.rebasedPath()); err != nil {
 				return err
 			}
@@ -166,7 +177,7 @@ func (vd *verDir) Remove(ctx context.Context, req *fuse.RemoveRequest) error {
 		node := vd.files[req.Name].node
 		ver := node.ver
 
-		if node.flags&NodeFlagVer == NodeFlagVer {
+		if node.flags&NodeFlagNew == NodeFlagNew {
 			if err := os.Remove(node.rebasedPath()); err != nil {
 				return err
 			}
@@ -183,6 +194,9 @@ func (vd *verDir) Remove(ctx context.Context, req *fuse.RemoveRequest) error {
 
 // NodeRequestLookuper
 func (vd *verDir) Lookup(ctx context.Context, name string) (fs.Node, error) {
+	vd.mutex.Lock()
+	defer vd.mutex.Unlock()
+
 	if dir, ok := vd.dirs[name]; ok {
 		return dir, nil
 	}
@@ -196,6 +210,9 @@ func (vd *verDir) Lookup(ctx context.Context, name string) (fs.Node, error) {
 
 // HandleReadDirAller
 func (vd *verDir) ReadDirAll(ctx context.Context) ([]fuse.Dirent, error) {
+	vd.mutex.Lock()
+	defer vd.mutex.Unlock()
+
 	entries := []fuse.Dirent{{Inode: vd.inode, Name: ".", Type: fuse.DT_Dir}}
 	if vd.parent != nil {
 		entry := fuse.Dirent{Inode: vd.parent.inode, Name: "..", Type: fuse.DT_Dir}
diff --git a/file.go b/file.go
index 0ba07d1..68ddd22 100644
--- a/file.go
+++ b/file.go
@@ -24,6 +24,7 @@ package main
 
 import (
 	"os"
+	"sync"
 
 	"bazil.org/fuse"
 	"bazil.org/fuse/fs"
@@ -34,24 +35,28 @@ import (
 //	verFile
 //
 
+type handleMap map[fuse.HandleID]*verFileHandle
+
 type verFile struct {
 	node    *verNode
 	inode   uint64
 	parent  *verDir
-	handles map[uint64]*verFileHandle
+	handles handleMap
+	mutex   sync.Mutex
 }
 
 func newVerFile(node *verNode, parent *verDir) *verFile {
-	return &verFile{node, allocInode(), parent, make(map[uint64]*verFileHandle)}
+	handles := make(handleMap)
+	mutex := sync.Mutex{}
+	return &verFile{node, allocInode(), parent, handles, mutex}
 }
 
 func (vf *verFile) version() error {
-	if vf.node.flags&NodeFlagVer == NodeFlagVer {
+	if vf.node.flags&NodeFlagNew == NodeFlagNew {
 		return nil
 	}
 
-	node := newVerNode(vf.node.path, vf.node.ver.db.lastVersion(), vf.node, NodeFlagVer)
-
+	node := newVerNode(vf.node.path, vf.node.ver.db.lastVersion(), vf.node, NodeFlagNew)
 	if _, err := copyFile(vf.node.rebasedPath(), node.rebasedPath()); err != nil {
 		return err
 	}
@@ -62,10 +67,13 @@ func (vf *verFile) version() error {
 	return nil
 }
 
-func (vf *verFile) open(flags fuse.OpenFlags, mode os.FileMode) (*verFileHandle, error) {
+func (vf *verFile) open(flags fuse.OpenFlags, mode os.FileMode) (*verFileHandle, fuse.HandleID, error) {
+	vf.mutex.Lock()
+	defer vf.mutex.Unlock()
+
 	if !flags.IsReadOnly() {
 		if err := vf.version(); err != nil {
-			return nil, err
+			return nil, 0, err
 		}
 	}
 
@@ -73,18 +81,20 @@ func (vf *verFile) open(flags fuse.OpenFlags, mode os.FileMode) (*verFileHandle,
 
 	handle, err := os.OpenFile(path, int(flags), mode)
 	if err != nil {
-		return nil, err
+		return nil, 0, err
 	}
 
 	id := allocHandleId()
-	verHandle := &verFileHandle{vf, path, handle, id}
+	verHandle := &verFileHandle{vf, path, handle}
 	vf.handles[id] = verHandle
 
-	return verHandle, nil
+	return verHandle, id, nil
 }
 
-func (vf *verFile) release(handle uint64) {
+func (vf *verFile) release(handle fuse.HandleID) {
+	vf.mutex.Lock()
 	delete(vf.handles, handle)
+	vf.mutex.Unlock()
 }
 
 // Node
@@ -106,23 +116,20 @@ func (vf *verFile) Setattr(ctx context.Context, req *fuse.SetattrRequest, resp *
 
 // NodeOpener
 func (vf *verFile) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenResponse) (fs.Handle, error) {
-	handle, err := vf.open(req.Flags, 0644)
+	handle, id, err := vf.open(req.Flags, 0644)
 	if err != nil {
 		return nil, err
 	}
 
+	resp.Handle = id
 	return handle, nil
 }
 
 // NodeFsyncer
 func (vf *verFile) Fsync(ctx context.Context, req *fuse.FsyncRequest) error {
-	for _, vfh := range vf.handles {
-		if err := vfh.handle.Sync(); err != nil {
-			return err
-		}
-	}
-
-	return nil
+	vf.mutex.Lock()
+	defer vf.mutex.Unlock()
+	return vf.handles[req.Handle].handle.Sync()
 }
 
 //
@@ -133,7 +140,6 @@ type verFileHandle struct {
 	node   *verFile
 	path   string
 	handle *os.File
-	id     uint64
 }
 
 // HandleReader
@@ -177,6 +183,6 @@ func (vfh *verFileHandle) Release(ctx context.Context, req *fuse.ReleaseRequest)
 	vfh.handle.Close()
 	vfh.handle = nil
 
-	vfh.node.release(vfh.id)
+	vfh.node.release(req.Handle)
 	return nil
 }
diff --git a/node.go b/node.go
index afd06c7..6e30c0d 100644
--- a/node.go
+++ b/node.go
@@ -36,7 +36,7 @@ import (
 
 const (
 	NodeFlagDir = 1 << iota
-	NodeFlagVer
+	NodeFlagNew
 )
 
 type verNode struct {
diff --git a/util.go b/util.go
index 9950607..68c2441 100644
--- a/util.go
+++ b/util.go
@@ -32,6 +32,8 @@ import (
 	"strconv"
 	"sync/atomic"
 	"time"
+
+	"bazil.org/fuse"
 )
 
 var inodeCnt, handleCnt uint64
@@ -40,8 +42,8 @@ func allocInode() uint64 {
 	return atomic.AddUint64(&inodeCnt, 1)
 }
 
-func allocHandleId() uint64 {
-	return atomic.AddUint64(&handleCnt, 1)
+func allocHandleId() fuse.HandleID {
+	return fuse.HandleID(atomic.AddUint64(&handleCnt, 1))
 }
 
 func copyFile(src, dst string) (int64, error) {