diff --git a/src/api.ml b/src/api.ml
index 074149bc..8a132db1 100644
--- a/src/api.ml
+++ b/src/api.ml
@@ -3,6 +3,7 @@
    normalized JSON-object
      for signature of ExchangeKeysResponse.exetensions field
    option: correct use opt_mem or Jsont.option
+   properly combine jsont for "interface DenomGroupRsa extends DenomGroupCommon"
    better types:
      - payto_uri
      - uri