diff --git a/exercises/practice/gigasecond/.docs/instructions.append.md b/exercises/practice/gigasecond/.docs/instructions.append.md
index 141df047d8..4faa77522c 100644
--- a/exercises/practice/gigasecond/.docs/instructions.append.md
+++ b/exercises/practice/gigasecond/.docs/instructions.append.md
@@ -1,3 +1,9 @@
 # Instructions append
 
+## Notes
+
+The input and output of the `gigasecond` function is of type [Date][date-link].
+
 It is possible to return a correct value for this exercise by mutating the solution function argument. Although there are legitimate use cases for mutating function arguments, this is usually undesirable, and in the case of this exercise, clearly unexpected. For this reason, the test suite has a test that fails in case the argument has been modified after the function execution.
+
+[date-link]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date