What version of protobuf and what language are you using?
Version: v1.4.2

What did you do?
https://github.com/AlekSi/go-bug/tree/master/jsonpb

func TestDuration(t *testing.T) {
	d := -time.Nanosecond
	dp := ptypes.DurationProto(d)
	m := &jsonpb.Marshaler{}
	s, err := m.MarshalToString(dp)
	if err != nil {
		t.Fatal(err)
	}
	if s != `"-0.000000001s"` {
		t.Errorf("Unexpected result: %s", s)
	}
}

What did you expect to see?
"-0.000000001s"

What did you see instead?
Unexpected result: "0.-00000001s"

Anything else we should know about your project / environment?
Issue #883 is back for 1.4.2.