diff --git a/schema_clusters.json b/schema_clusters.json
index 7f78501..7ce7d7d 100644
--- a/schema_clusters.json
+++ b/schema_clusters.json
@@ -132,7 +132,13 @@
                 "items": {
                   "type": "string"
                 }
-              }
+              },
+              "official-refs": {
+                "type": "array",
+                "uniqueItems": true,
+                "items": {
+                  "type": "string"
+                }
             }
           }
         },