diff --git a/hphp/hack/manual/hack/08-arrays-and-collections/05-vec-keyset-and-dict.md b/hphp/hack/manual/hack/08-arrays-and-collections/05-vec-keyset-and-dict.md
index babb37cbe50e2d..44d9c054575a30 100644
--- a/hphp/hack/manual/hack/08-arrays-and-collections/05-vec-keyset-and-dict.md
+++ b/hphp/hack/manual/hack/08-arrays-and-collections/05-vec-keyset-and-dict.md
@@ -79,7 +79,8 @@ $items is vec<_>; // true
 A `keyset` is an ordered data structure without duplicates. It is
 created with the `keyset[]` syntax.
 
-A `keyset` can only contain `string` or `int` values.
+A `keyset` can only contain `string` or `int` values. `keyset`s are
+ordered according to the insertion order.
 
 
 ```Hack