diff --git a/proxy/handler.go b/proxy/handler.go
index 752f892..e988ddf 100644
--- a/proxy/handler.go
+++ b/proxy/handler.go
@@ -9,6 +9,8 @@ import (
 	"golang.org/x/net/context"
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
+	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/status"
 )
 
 var (
@@ -70,7 +72,18 @@ func (s *handler) handler(srv interface{}, serverStream grpc.ServerStream) error
 	}
 
 	clientCtx, clientCancel := context.WithCancel(outgoingCtx)
-	// TODO(mwitkow): Add a `forwarded` header to metadata, https://en.wikipedia.org/wiki/X-Forwarded-For.
+	md, ok := metadata.FromIncomingContext(clientCtx)
+	if !ok {
+		return status.Error(codes.Internal, ":authority header has not been set")
+	}
+	authority, ok := md[":authority"]
+	if !ok {
+		return status.Error(codes.Internal, ":authority header has not been set")
+	}
+	md = md.Copy() // metadata is immutable, copy.
+	md["x-forwarded-host"] = authority
+
+	clientCtx = metadata.NewOutgoingContext(clientCtx, md)
 	clientStream, err := grpc.NewClientStream(clientCtx, clientStreamDescForProxying, backendConn, fullMethodName)
 	if err != nil {
 		return err
diff --git a/proxy/handler_test.go b/proxy/handler_test.go
index c811408..e48fb97 100644
--- a/proxy/handler_test.go
+++ b/proxy/handler_test.go
@@ -4,6 +4,7 @@
 package proxy_test
 
 import (
+	"fmt"
 	"io"
 	"log"
 	"net"
@@ -13,6 +14,7 @@ import (
 	"time"
 
 	"github.com/mwitkow/grpc-proxy/proxy"
+	pb "github.com/mwitkow/grpc-proxy/testservice"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"github.com/stretchr/testify/suite"
@@ -21,10 +23,6 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/grpclog"
 	"google.golang.org/grpc/metadata"
-
-	"fmt"
-
-	pb "github.com/mwitkow/grpc-proxy/testservice"
 )
 
 const (