diff --git a/src/test/java/org/cactoos/number/SumOfTest.java b/src/test/java/org/cactoos/number/SumOfTest.java
index 2011744b8..3c4d287f9 100644
--- a/src/test/java/org/cactoos/number/SumOfTest.java
+++ b/src/test/java/org/cactoos/number/SumOfTest.java
@@ -34,6 +34,11 @@
  * Test case for {@link SumOf}.
  *
  * @since 0.9
+ * @todo #1335:30min Following the rewrite of the Number implementations
+ *  in cactoos, the three methods below prefixed by overflow where adapted
+ *  because they started to give different results. The task is to investigate
+ *  thoroughly what is a "correct" behaviour concerning overflow in the case
+ *  of SumOf and adapt the tests and the code to make this obvious and clear.
  * @checkstyle JavadocMethodCheck (500 lines)
  * @checkstyle MagicNumberCheck (500 lines)
  */