diff --git a/runtime/handler_test.go b/runtime/handler_test.go
index 4ef78e7f0ef..34d70539f6e 100644
--- a/runtime/handler_test.go
+++ b/runtime/handler_test.go
@@ -178,36 +178,68 @@ func (c *CustomMarshaler) NewDecoder(r io.Reader) runtime.Decoder     { return c
 func (c *CustomMarshaler) NewEncoder(w io.Writer) runtime.Encoder     { return c.m.NewEncoder(w) }
 func (c *CustomMarshaler) ContentType(v interface{}) string           { return "Custom-Content-Type" }
 
+// marshalerStreamContentType implements Marshaler, but with the addition of a custom StreamContentType.
+type marshalerStreamContentType struct {
+	runtime.Marshaler
+	CustomStreamContentType string
+}
+
+func (m marshalerStreamContentType) StreamContentType(interface{}) string {
+	return m.CustomStreamContentType
+}
+
 func TestForwardResponseStreamCustomMarshaler(t *testing.T) {
 	type msg struct {
 		pb  proto.Message
 		err error
 	}
+	marshaler := &CustomMarshaler{&runtime.JSONPb{}}
+
 	tests := []struct {
-		name       string
-		msgs       []msg
-		statusCode int
+		name            string
+		marshaler       runtime.Marshaler
+		msgs            []msg
+		statusCode      int
+		wantContentType string
 	}{{
-		name: "encoding",
+		name:      "encoding",
+		marshaler: marshaler,
 		msgs: []msg{
 			{&pb.SimpleMessage{Id: "One"}, nil},
 			{&pb.SimpleMessage{Id: "Two"}, nil},
 		},
-		statusCode: http.StatusOK,
+		statusCode:      http.StatusOK,
+		wantContentType: "Custom-Content-Type",
 	}, {
 		name:       "empty",
+		marshaler:  marshaler,
 		statusCode: http.StatusOK,
 	}, {
-		name:       "error",
-		msgs:       []msg{{nil, status.Errorf(codes.OutOfRange, "400")}},
-		statusCode: http.StatusBadRequest,
+		name:            "error",
+		marshaler:       marshaler,
+		msgs:            []msg{{nil, status.Errorf(codes.OutOfRange, "400")}},
+		statusCode:      http.StatusBadRequest,
+		wantContentType: "Custom-Content-Type",
 	}, {
-		name: "stream_error",
+		name:      "stream_error",
+		marshaler: marshaler,
 		msgs: []msg{
 			{&pb.SimpleMessage{Id: "One"}, nil},
 			{nil, status.Errorf(codes.OutOfRange, "400")},
 		},
-		statusCode: http.StatusOK,
+		statusCode:      http.StatusOK,
+		wantContentType: "Custom-Content-Type",
+	}, {
+		name: "stream_content_type",
+		marshaler: marshalerStreamContentType{
+			Marshaler:               marshaler,
+			CustomStreamContentType: "Stream-Content-Type",
+		},
+		msgs: []msg{
+			{&pb.SimpleMessage{Id: "One"}, nil},
+		},
+		statusCode:      http.StatusOK,
+		wantContentType: "Stream-Content-Type",
 	}}
 
 	newTestRecv := func(t *testing.T, msgs []msg) func() (proto.Message, error) {
@@ -224,14 +256,13 @@ func TestForwardResponseStreamCustomMarshaler(t *testing.T) {
 		}
 	}
 	ctx := runtime.NewServerMetadataContext(context.Background(), runtime.ServerMetadata{})
-	marshaler := &CustomMarshaler{&runtime.JSONPb{}}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			recv := newTestRecv(t, tt.msgs)
 			req := httptest.NewRequest("GET", "http://example.com/foo", nil)
 			resp := httptest.NewRecorder()
 
-			runtime.ForwardResponseStream(ctx, runtime.NewServeMux(), marshaler, resp, req, recv)
+			runtime.ForwardResponseStream(ctx, runtime.NewServeMux(), tt.marshaler, resp, req, recv)
 
 			w := resp.Result()
 			if w.StatusCode != tt.statusCode {
@@ -245,8 +276,8 @@ func TestForwardResponseStreamCustomMarshaler(t *testing.T) {
 				t.Errorf("Failed to read response body with %v", err)
 			}
 			w.Body.Close()
-			if len(body) > 0 && w.Header.Get("Content-Type") != "Custom-Content-Type" {
-				t.Errorf("Content-Type %s want Custom-Content-Type", w.Header.Get("Content-Type"))
+			if w.Header.Get("Content-Type") != tt.wantContentType {
+				t.Errorf("Content-Type %q want %q", w.Header.Get("Content-Type"), tt.wantContentType)
 			}
 
 			var want []byte
@@ -254,7 +285,7 @@ func TestForwardResponseStreamCustomMarshaler(t *testing.T) {
 				if msg.err != nil {
 					t.Skip("checking error encodings")
 				}
-				b, err := marshaler.Marshal(map[string]proto.Message{"result": msg.pb})
+				b, err := tt.marshaler.Marshal(map[string]proto.Message{"result": msg.pb})
 				if err != nil {
 					t.Errorf("marshaler.Marshal() failed %v", err)
 				}