diff --git a/meta_flags.go b/meta_flags.go
index f5c7b81..b071243 100644
--- a/meta_flags.go
+++ b/meta_flags.go
@@ -13,11 +13,6 @@ func buildMetaFlags(fs []metaFlag) string {
 }
 
 func obtainMetaFlagsResults(ss []string) (mr MetaResult, err error) {
-	// Always set the cas token as setted
-	// enforce the operation use this token always use the CasToken.value
-	// even if the token is not returned.
-	// To avoid unexpected non-cas opertion caused by the lack of "c" flag.
-	mr.CasToken.setted = true
 	for _, f := range ss {
 		k, v := f[0], f[1:]
 		switch k {
@@ -32,7 +27,9 @@ func obtainMetaFlagsResults(ss []string) (mr MetaResult, err error) {
 		case 'O':
 			mr.Opaque = v
 		case 'c':
-			mr.CasToken.value, err = strconv.ParseInt(v, 10, 64)
+			var cv int64
+			cv, err = strconv.ParseInt(v, 10, 64)
+			mr.CasToken = casToken(cv)
 		case 'f':
 			v, err := strconv.ParseUint(v, 10, 32)
 			if err != nil {
diff --git a/meta_options.go b/meta_options.go
index ffc9c2d..6ff3a05 100644
--- a/meta_options.go
+++ b/meta_options.go
@@ -1,8 +1,13 @@
 package memcache
 
-type casToken struct {
-	value  int64
-	setted bool
+type CasToken interface {
+	value() int64
+}
+
+type casToken int64
+
+func (c casToken) value() int64 {
+	return int64(c)
 }
 
 type MetaGetOptions struct {
@@ -79,7 +84,7 @@ type MetaSetOptions struct {
 	Key       string   // the key of item
 	BinaryKey []byte   // interpret key as base64 encoded binary value (see metaget)
 	Value     []byte   // the value of item
-	CasToken  casToken // compare and swap token
+	CasToken  CasToken // compare and swap token
 
 	GetCasToken bool // return CAS value if successfully stored.
 
@@ -109,8 +114,8 @@ func (o MetaSetOptions) marshal() (fs []metaFlag) {
 	if o.SetTTL != 0 {
 		fs = append(fs, withSetTTL(o.SetTTL))
 	}
-	if o.CasToken.setted {
-		fs = append(fs, withCompareCAS(o.CasToken.value))
+	if o.CasToken != nil {
+		fs = append(fs, withCompareCAS(o.CasToken.value()))
 	}
 	return
 }
@@ -118,7 +123,7 @@ func (o MetaSetOptions) marshal() (fs []metaFlag) {
 type MetaDeletOptions struct {
 	Key       string   // the key of item
 	BinaryKey []byte   // interpret key as base64 encoded binary value (see metaget)
-	CasToken  casToken // compare and swap token
+	CasToken  CasToken // compare and swap token
 
 	SetTTL        uint64 // updates TTL, only when paired with the SetInvalidate option
 	SetInvalidate bool   // mark as stale, bumps CAS.
@@ -134,8 +139,8 @@ func (o MetaDeletOptions) marshal() (fs []metaFlag) {
 	if o.SetTTL != 0 {
 		fs = append(fs, withSetTTL(o.SetTTL))
 	}
-	if o.CasToken.setted {
-		fs = append(fs, withCompareCAS(o.CasToken.value))
+	if o.CasToken != nil {
+		fs = append(fs, withCompareCAS(o.CasToken.value()))
 	}
 	return
 }
@@ -151,7 +156,7 @@ const (
 type MetaArithmeticOptions struct {
 	Key       string   // the key of item
 	BinaryKey []byte   // interpret key as base64 encoded binary value (see metaget)
-	CasToken  casToken // compare and swap token
+	CasToken  CasToken // compare and swap token
 
 	GetCasToken bool // return current CAS value if successful.
 	GetTTL      bool // return current TTL
@@ -193,8 +198,8 @@ func (o MetaArithmeticOptions) marshal() (fs []metaFlag) {
 	if o.SetTTL != 0 {
 		fs = append(fs, withSetTTL(o.SetTTL))
 	}
-	if o.CasToken.setted {
-		fs = append(fs, withCompareCAS(o.CasToken.value))
+	if o.CasToken != nil {
+		fs = append(fs, withCompareCAS(o.CasToken.value()))
 	}
 	return
 }
diff --git a/meta_test.go b/meta_test.go
index ecd1557..f5c14fd 100644
--- a/meta_test.go
+++ b/meta_test.go
@@ -30,7 +30,7 @@ func TestMetaSetGet(t *testing.T) {
 	if err != nil {
 		t.Error(err)
 	}
-	if sr.CasToken.value == 0 {
+	if int(sr.CasToken) == 0 {
 		t.Error("CAS Incorrect")
 	}
 
@@ -127,7 +127,7 @@ func TestMetaSetCAS(t *testing.T) {
 	_, err = c.MetaSet(ctx, MetaSetOptions{
 		Key:      k,
 		Value:    v,
-		CasToken: casToken{0, true},
+		CasToken: casToken(0),
 	})
 	if err != ErrCASConflict {
 		t.Error("CAS Invalid")
@@ -279,3 +279,30 @@ func TestBinaryKey(t *testing.T) {
 		t.Error("Binary Key Error.", err)
 	}
 }
+
+func TestMetaCasMiss(t *testing.T) {
+	c, _ := New(os.Getenv("MC_ADDRESS"), 2, 100)
+
+	ctx := context.Background()
+	k := "MEI"
+	var ttl uint64 = 20
+
+	item, err := c.MetaGet(ctx, MetaGetOptions{
+		Key:              k,
+		SetVivifyWithTTL: ttl,
+		GetValue:         true,
+	})
+	if err != nil {
+		t.Error(err)
+	}
+
+	item, err = c.MetaSet(ctx, MetaSetOptions{
+		Key:      k,
+		CasToken: item.CasToken,
+		Value:    []byte("t"),
+	})
+	if err != ErrCASConflict {
+		t.Errorf("CAS Error")
+	}
+
+}