diff --git a/vendor/google.golang.org/grpc/credentials/credentials.go b/vendor/google.golang.org/grpc/credentials/credentials.go
index a851560..8ea3d4a 100644
--- a/vendor/google.golang.org/grpc/credentials/credentials.go
+++ b/vendor/google.golang.org/grpc/credentials/credentials.go
@@ -36,9 +36,6 @@
 	"google.golang.org/grpc/credentials/internal"
 )
 
-// alpnProtoStr are the specified application level protocols for gRPC.
-var alpnProtoStr = []string{"h2"}
-
 // PerRPCCredentials defines the common interface for the credentials which need to
 // attach security information to every RPC (e.g., oauth2).
 type PerRPCCredentials interface {
@@ -208,10 +205,23 @@
 	return nil
 }
 
+const alpnProtoStrH2 = "h2"
+
+func appendH2ToNextProtos(ps []string) []string {
+	for _, p := range ps {
+		if p == alpnProtoStrH2 {
+			return ps
+		}
+	}
+	ret := make([]string, 0, len(ps)+1)
+	ret = append(ret, ps...)
+	return append(ret, alpnProtoStrH2)
+}
+
 // NewTLS uses c to construct a TransportCredentials based on TLS.
 func NewTLS(c *tls.Config) TransportCredentials {
 	tc := &tlsCreds{cloneTLSConfig(c)}
-	tc.config.NextProtos = alpnProtoStr
+	tc.config.NextProtos = appendH2ToNextProtos(tc.config.NextProtos)
 	return tc
 }
 
@@ -268,24 +278,22 @@
 // TLSChannelzSecurityValue defines the struct that TLS protocol should return
 // from GetSecurityValue(), containing security info like cipher and certificate used.
 type TLSChannelzSecurityValue struct {
+	ChannelzSecurityValue
 	StandardName      string
 	LocalCertificate  []byte
 	RemoteCertificate []byte
 }
 
-func (*TLSChannelzSecurityValue) isChannelzSecurityValue() {}
-
 // OtherChannelzSecurityValue defines the struct that non-TLS protocol should return
 // from GetSecurityValue(), which contains protocol specific security info. Note
 // the Value field will be sent to users of channelz requesting channel info, and
 // thus sensitive info should better be avoided.
 type OtherChannelzSecurityValue struct {
+	ChannelzSecurityValue
 	Name  string
 	Value proto.Message
 }
 
-func (*OtherChannelzSecurityValue) isChannelzSecurityValue() {}
-
 var cipherSuiteLookup = map[uint16]string{
 	tls.TLS_RSA_WITH_RC4_128_SHA:                "TLS_RSA_WITH_RC4_128_SHA",
 	tls.TLS_RSA_WITH_3DES_EDE_CBC_SHA:           "TLS_RSA_WITH_3DES_EDE_CBC_SHA",