diff --git a/smime.go b/smime.go
index e92d283..ae6e4f2 100644
--- a/smime.go
+++ b/smime.go
@@ -16,6 +16,9 @@ var (
 	// ErrInvalidKeyPair should be used if key pair is invalid
 	ErrInvalidKeyPair = errors.New("invalid key pair")
 
+	// ErrInvalidParentCertificates should be used if one of the parent certificates is invalid
+	ErrInvalidParentCertificates = errors.New("invalid parent certificates")
+
 	// ErrCouldNotInitialize should be used if the signed data could not initialize
 	ErrCouldNotInitialize = errors.New("could not initialize signed data")
 
@@ -31,8 +34,9 @@ var (
 
 // SMime is used to sign messages with S/MIME
 type SMime struct {
-	privateKey  *rsa.PrivateKey
-	certificate *x509.Certificate
+	privateKey         *rsa.PrivateKey
+	parentCertificates []*x509.Certificate
+	certificate        *x509.Certificate
 }
 
 // NewSMime construct a new instance of SMime with a provided *tls.Certificate
@@ -41,9 +45,19 @@ func newSMime(keyPair *tls.Certificate) (*SMime, error) {
 		return nil, ErrInvalidKeyPair
 	}
 
+	parentCertificates := make([]*x509.Certificate, 0)
+	for _, cert := range keyPair.Certificate[1:] {
+		c, err := x509.ParseCertificate(cert)
+		if err != nil {
+			return nil, ErrInvalidParentCertificates
+		}
+		parentCertificates = append(parentCertificates, c)
+	}
+
 	return &SMime{
-		privateKey:  keyPair.PrivateKey.(*rsa.PrivateKey),
-		certificate: keyPair.Leaf,
+		privateKey:         keyPair.PrivateKey.(*rsa.PrivateKey),
+		certificate:        keyPair.Leaf,
+		parentCertificates: parentCertificates,
 	}, nil
 }
 
@@ -58,7 +72,7 @@ func (sm *SMime) signMessage(message string) (*string, error) {
 		return nil, ErrCouldNotInitialize
 	}
 
-	if err = signedData.AddSigner(sm.certificate, sm.privateKey, pkcs7.SignerInfoConfig{}); err != nil {
+	if err = signedData.AddSignerChain(sm.certificate, sm.privateKey, sm.parentCertificates, pkcs7.SignerInfoConfig{}); err != nil {
 		return nil, ErrCouldNotAddSigner
 	}