diff --git a/include/caosdb/entity.h b/include/caosdb/entity.h
index 2f662e06a83e0877746ffdf85587edc6be03236d..a96126e1b705ff741527d77fd285946395487299 100644
--- a/include/caosdb/entity.h
+++ b/include/caosdb/entity.h
@@ -203,6 +203,7 @@ private:
   public:
     explicit iterator(const RepeatedPtrFieldWrapper<T, P> *instance,
                       int index = 0);
+    // TODO(henrik) add unit tests
     auto operator*() const -> T &;
     auto operator++() -> iterator &;
     auto operator++(int) -> iterator;