diff --git a/nomenclature.yaml b/nomenclature.yaml
index 63ba550..09871ec 100644
--- a/nomenclature.yaml
+++ b/nomenclature.yaml
@@ -17,6 +17,7 @@ definitions:
         - hierarchy: R9
         - hierarchy: R10
         - hierarchy: G20 Members
+        - hierarchy: Regional Organizations
         - hierarchy: MESSAGEix-GLOBIOM 2.1-R12
         - hierarchy: AIM 3.0
         - hierarchy: COFFEE 1.6