diff --git a/src/mint-lib/mint_api_refresh.c b/src/mint-lib/mint_api_refresh.c
index d8391ac4a..442a73e1a 100644
--- a/src/mint-lib/mint_api_refresh.c
+++ b/src/mint-lib/mint_api_refresh.c
@@ -519,7 +519,7 @@ serialize_denomination_key (const struct TALER_DenominationPublicKey *dk,
           pbuf,
           pbuf_size);
   GNUNET_free (pbuf);
-  return pbuf_size;
+  return pbuf_size + sizeof (uint32_t);
 }