diff --git a/credentials/credentials.go b/credentials/credentials.go
index a851560456b4..88aff94596a1 100644
--- a/credentials/credentials.go
+++ b/credentials/credentials.go
@@ -36,9 +36,6 @@ import (
 	"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 @@ func (c *tlsCreds) OverrideServerName(serverNameOverride string) error {
 	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
 }
 
diff --git a/credentials/credentials_test.go b/credentials/credentials_test.go
index cb091de08092..b15458636f1a 100644
--- a/credentials/credentials_test.go
+++ b/credentials/credentials_test.go
@@ -22,6 +22,7 @@ import (
 	"context"
 	"crypto/tls"
 	"net"
+	"reflect"
 	"testing"
 
 	"google.golang.org/grpc/testdata"
@@ -204,3 +205,39 @@ func tlsClientHandshake(conn net.Conn, _ string) (AuthInfo, error) {
 	}
 	return TLSInfo{State: clientConn.ConnectionState()}, nil
 }
+
+func TestAppendH2ToNextProtos(t *testing.T) {
+	tests := []struct {
+		name string
+		ps   []string
+		want []string
+	}{
+		{
+			name: "empty",
+			ps:   nil,
+			want: []string{"h2"},
+		},
+		{
+			name: "only h2",
+			ps:   []string{"h2"},
+			want: []string{"h2"},
+		},
+		{
+			name: "with h2",
+			ps:   []string{"alpn", "h2"},
+			want: []string{"alpn", "h2"},
+		},
+		{
+			name: "no h2",
+			ps:   []string{"alpn"},
+			want: []string{"alpn", "h2"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := appendH2ToNextProtos(tt.ps); !reflect.DeepEqual(got, tt.want) {
+				t.Errorf("appendH2ToNextProtos() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}