diff --git a/runtime/handler.go b/runtime/handler.go
index 8fe6a77efd5..63dc812b781 100644
--- a/runtime/handler.go
+++ b/runtime/handler.go
@@ -6,6 +6,7 @@ import (
 	"io"
 	"net/http"
 	"net/textproto"
+	"strconv"
 	"strings"
 
 	"google.golang.org/genproto/googleapis/api/httpbody"
@@ -176,6 +177,10 @@ func ForwardResponseMessage(ctx context.Context, mux *ServeMux, marshaler Marsha
 		return
 	}
 
+	if !doForwardTrailers {
+		w.Header().Set("Content-Length", strconv.Itoa(len(buf)))
+	}
+
 	if _, err = w.Write(buf); err != nil {
 		grpclog.Infof("Failed to write response: %v", err)
 	}
diff --git a/runtime/handler_test.go b/runtime/handler_test.go
index 88f4a92a5b4..b0ad6e2c90d 100644
--- a/runtime/handler_test.go
+++ b/runtime/handler_test.go
@@ -339,6 +339,7 @@ func TestOutgoingHeaderMatcher(t *testing.T) {
 				),
 			},
 			headers: http.Header{
+				"Content-Length":    []string{"12"},
 				"Content-Type":      []string{"application/json"},
 				"Grpc-Metadata-Foo": []string{"bar"},
 				"Grpc-Metadata-Baz": []string{"qux"},
@@ -353,8 +354,9 @@ func TestOutgoingHeaderMatcher(t *testing.T) {
 				),
 			},
 			headers: http.Header{
-				"Content-Type": []string{"application/json"},
-				"Custom-Foo":   []string{"bar"},
+				"Content-Length": []string{"12"},
+				"Content-Type":   []string{"application/json"},
+				"Custom-Foo":     []string{"bar"},
 			},
 			matcher: func(key string) (string, bool) {
 				switch key {
@@ -412,8 +414,9 @@ func TestOutgoingTrailerMatcher(t *testing.T) {
 				"Te": []string{"trailers"},
 			},
 			headers: http.Header{
-				"Content-Type": []string{"application/json"},
-				"Trailer":      []string{"Grpc-Trailer-Foo,Grpc-Trailer-Baz"},
+				"Transfer-Encoding": []string{"chunked"},
+				"Content-Type":      []string{"application/json"},
+				"Trailer":           []string{"Grpc-Trailer-Foo", "Grpc-Trailer-Baz"},
 			},
 			trailer: http.Header{
 				"Grpc-Trailer-Foo": []string{"bar"},
@@ -429,7 +432,8 @@ func TestOutgoingTrailerMatcher(t *testing.T) {
 				),
 			},
 			headers: http.Header{
-				"Content-Type": []string{"application/json"},
+				"Content-Length": []string{"12"},
+				"Content-Type":   []string{"application/json"},
 			},
 		},
 		{
@@ -444,8 +448,9 @@ func TestOutgoingTrailerMatcher(t *testing.T) {
 				"Te": []string{"trailers"},
 			},
 			headers: http.Header{
-				"Content-Type": []string{"application/json"},
-				"Trailer":      []string{"Custom-Trailer-Foo"},
+				"Transfer-Encoding": []string{"chunked"},
+				"Content-Type":      []string{"application/json"},
+				"Trailer":           []string{"Custom-Trailer-Foo"},
 			},
 			trailer: http.Header{
 				"Custom-Trailer-Foo": []string{"bar"},
@@ -478,6 +483,10 @@ func TestOutgoingTrailerMatcher(t *testing.T) {
 				t.Fatalf("StatusCode %d want %d", w.StatusCode, http.StatusOK)
 			}
 
+			if !reflect.DeepEqual(w.Header, tc.headers) {
+				t.Fatalf("Header %v want %v", w.Header, tc.headers)
+			}
+
 			if !reflect.DeepEqual(w.Trailer, tc.trailer) {
 				t.Fatalf("Trailer %v want %v", w.Trailer, tc.trailer)
 			}