diff --git a/dkim.go b/dkim.go
index 3c270aa..123c6e0 100644
--- a/dkim.go
+++ b/dkim.go
@@ -16,7 +16,7 @@ import (
 	"io/ioutil"
 	"regexp"
 	"strings"
-	"time"
+	//"time"
 )
 
 const (
@@ -66,7 +66,7 @@ type sigOptions struct {
 	AddSignatureTimestamp bool
 
 	// Time validity of the signature (0=never)
-	SignatureExpireIn time.Duration
+	SignatureExpireIn uint64
 
 	// CopiedHeaderFileds
 	CopiedHeaderFileds []string
@@ -82,7 +82,7 @@ func NewSigOptions() sigOptions {
 		BodyLength:            0,
 		QueryMethods:          []string{"dns/txt"},
 		AddSignatureTimestamp: false,
-		SignatureExpireIn:     0 * time.Second,
+		SignatureExpireIn:     0,
 	}
 }
 
diff --git a/dkimHeader.go b/dkimHeader.go
index 5908a7c..b0d6da7 100644
--- a/dkimHeader.go
+++ b/dkimHeader.go
@@ -198,8 +198,9 @@ func NewDkimHeaderBySigOptions(options sigOptions) *DkimHeader {
 	if options.AddSignatureTimestamp {
 		h.SignatureTimestamp = time.Now()
 	}
-	if options.SignatureExpireIn.Seconds() > 0 {
-		h.SignatureExpiration = time.Now().Add(options.SignatureExpireIn)
+	if options.SignatureExpireIn > 0 {
+		fmt.Println(options.SignatureExpireIn)
+		h.SignatureExpiration = time.Now().Add(time.Duration(options.SignatureExpireIn) * time.Second)
 	}
 	h.CopiedHeaderFileds = options.CopiedHeaderFileds
 	return h
@@ -250,7 +251,6 @@ func (d *DkimHeader) GetHeaderBase(bodyHash string) string {
 			subh = ""
 		}
 		subh += " x=" + fmt.Sprintf("%d", ts) + ";"
-
 	}
 
 	// Headers
diff --git a/dkim_test.go b/dkim_test.go
index 1a0ce21..3bbdf11 100644
--- a/dkim_test.go
+++ b/dkim_test.go
@@ -172,8 +172,8 @@ func Test_Sign(t *testing.T) {
 	options.Canonicalization = "relaxed/relaxed"
 	options.Domain = domain
 	options.Selector = selector
-	//options.AddSignatureTimestamp = true
-	//options.SignatureExpireIn = 3600
+	options.AddSignatureTimestamp = true
+	options.SignatureExpireIn = 3600
 	options.Headers = []string{"from"}
 	emailReader, err := Sign(emailReader, options)
 	assert.NoError(t, err)