diff --git a/apis/validator/sync_committee_selections.yaml b/apis/validator/sync_committee_selections.yaml
index 0b26fb0b..857009fd 100644
--- a/apis/validator/sync_committee_selections.yaml
+++ b/apis/validator/sync_committee_selections.yaml
@@ -37,5 +37,7 @@ post:
       $ref: '../../beacon-node-oapi.yaml#/components/responses/InvalidRequest'
     "500":
       $ref: '../../beacon-node-oapi.yaml#/components/responses/InternalError'
+    "501":
+      $ref: '../../beacon-node-oapi.yaml#/components/responses/NotImplementedError'
     "503":
       $ref: '../../beacon-node-oapi.yaml#/components/responses/CurrentlySyncing'