diff --git a/src/hb-ot-var-avar-table.hh b/src/hb-ot-var-avar-table.hh
index e6280386c..a3b346e48 100644
--- a/src/hb-ot-var-avar-table.hh
+++ b/src/hb-ot-var-avar-table.hh
@@ -42,6 +42,7 @@
 namespace OT {
 
 
+/* "Spec": https://github.com/be-fonts/boring-expansion-spec/issues/14 */
 struct avarV2Tail
 {
   friend struct avar;