diff --git a/memfile.go b/memfile.go
index 50f148c..2e6751f 100644
--- a/memfile.go
+++ b/memfile.go
@@ -18,6 +18,7 @@
 	"bytes"
 	"io"
 	"os"
+	"sync"
 	"sync/atomic"
 )
 
@@ -32,6 +33,7 @@
 }
 
 type InMemoryFile struct {
+	sync.Mutex
 	at      int64
 	name    string
 	data    []byte
@@ -48,13 +50,17 @@
 
 func (f *InMemoryFile) Open() error {
 	atomic.StoreInt64(&f.at, 0)
+	f.Lock()
 	f.closed = false
+	f.Unlock()
 	return nil
 }
 
 func (f *InMemoryFile) Close() error {
 	atomic.StoreInt64(&f.at, 0)
+	f.Lock()
 	f.closed = true
+	f.Unlock()
 	return nil
 }
 
@@ -102,6 +108,8 @@
 }
 
 func (f *InMemoryFile) Read(b []byte) (n int, err error) {
+	f.Lock()
+	defer f.Unlock()
 	if f.closed == true {
 		return 0, ErrFileClosed
 	}
@@ -157,6 +165,8 @@
 func (f *InMemoryFile) Write(b []byte) (n int, err error) {
 	n = len(b)
 	cur := atomic.LoadInt64(&f.at)
+	f.Lock()
+	defer f.Unlock()
 	diff := cur - int64(len(f.data))
 	var tail []byte
 	if n+int(cur) < len(f.data) {