diff --git a/runtime/handler.go b/runtime/handler.go
index cdf5510d247..1770b85344d 100644
--- a/runtime/handler.go
+++ b/runtime/handler.go
@@ -41,6 +41,8 @@ func ForwardResponseStream(ctx context.Context, mux *ServeMux, marshaler Marshal
 	var delimiter []byte
 	if d, ok := marshaler.(Delimited); ok {
 		delimiter = d.Delimiter()
+	} else {
+	    delimiter = []byte("\n")
 	}
 
 	var wroteHeader bool
diff --git a/runtime/handler_test.go b/runtime/handler_test.go
index 344521c8a9c..493aa5e5495 100644
--- a/runtime/handler_test.go
+++ b/runtime/handler_test.go
@@ -102,3 +102,103 @@ func TestForwardResponseStream(t *testing.T) {
 		})
 	}
 }
+
+
+// A custom marshaler implementation, that doesn't implement the delimited interface
+type CustomMarshaler struct {
+    m *runtime.JSONPb
+}
+func (c *CustomMarshaler) Marshal(v interface{}) ([]byte, error) { return c.m.Marshal(v) }
+func (c *CustomMarshaler) Unmarshal(data []byte, v interface{}) error { return c.m.Unmarshal(data, v) }
+func (c *CustomMarshaler) NewDecoder(r io.Reader) runtime.Decoder { return c.m.NewDecoder(r) }
+func (c *CustomMarshaler) NewEncoder(w io.Writer) runtime.Encoder { return c.m.NewEncoder(w) }
+func (c *CustomMarshaler) ContentType() string { return c.m.ContentType() }
+
+
+func TestForwardResponseStreamCustomMarshaler(t *testing.T) {
+	type msg struct {
+		pb  proto.Message
+		err error
+	}
+	tests := []struct {
+		name       string
+		msgs       []msg
+		statusCode int
+	}{{
+		name: "encoding",
+		msgs: []msg{
+			{&pb.SimpleMessage{Id: "One"}, nil},
+			{&pb.SimpleMessage{Id: "Two"}, nil},
+		},
+		statusCode: http.StatusOK,
+	}, {
+		name:       "empty",
+		statusCode: http.StatusOK,
+	}, {
+		name:       "error",
+		msgs:       []msg{{nil, grpc.Errorf(codes.OutOfRange, "400")}},
+		statusCode: http.StatusBadRequest,
+	}, {
+		name: "stream_error",
+		msgs: []msg{
+			{&pb.SimpleMessage{Id: "One"}, nil},
+			{nil, grpc.Errorf(codes.OutOfRange, "400")},
+		},
+		statusCode: http.StatusOK,
+	}}
+
+	newTestRecv := func(t *testing.T, msgs []msg) func() (proto.Message, error) {
+		var count int
+		return func() (proto.Message, error) {
+			if count == len(msgs) {
+				return nil, io.EOF
+			} else if count > len(msgs) {
+				t.Errorf("recv() called %d times for %d messages", count, len(msgs))
+			}
+			count++
+			msg := msgs[count-1]
+			return msg.pb, msg.err
+		}
+	}
+	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)
+
+			w := resp.Result()
+			if w.StatusCode != tt.statusCode {
+				t.Errorf("StatusCode %d want %d", w.StatusCode, tt.statusCode)
+			}
+			if h := w.Header.Get("Transfer-Encoding"); h != "chunked" {
+				t.Errorf("ForwardResponseStream missing header chunked")
+			}
+			body, err := ioutil.ReadAll(w.Body)
+			if err != nil {
+				t.Errorf("Failed to read response body with %v", err)
+			}
+			w.Body.Close()
+
+			var want []byte
+			for _, msg := range tt.msgs {
+				if msg.err != nil {
+					t.Skip("checking erorr encodings")
+				}
+				b, err := marshaler.Marshal(map[string]proto.Message{"result": msg.pb})
+				if err != nil {
+					t.Errorf("marshaler.Marshal() failed %v", err)
+				}
+				want = append(want, b...)
+				want = append(want, "\n"...)
+			}
+
+			if string(body) != string(want) {
+				t.Errorf("ForwardResponseStream() = \"%s\" want \"%s\"", body, want)
+			}
+		})
+	}
+}