diff --git a/README.md b/README.md
index a48295c9..43b47ccc 100644
--- a/README.md
+++ b/README.md
@@ -356,6 +356,8 @@ The modules that ship with Scryer Prolog are also called
   providing `empty_assoc/1`, `get_assoc/3`, `put_assoc/4` etc.
   to manage elements in AVL trees which ensure
   *O*(log(*N*)) access.
+* [`ordsets`](src/prolog/lib/ordsets.pl)
+  represents ordered sets as lists.
 * [`clpb`](src/prolog/lib/clpb.pl)
   CLP(B): Constraint Logic Programming over Boolean variables,
   a BDD-based SAT solver provided via the predicates