diff --git a/src/include/taler_signatures.h b/src/include/taler_signatures.h
index 9ef50d1d3..de6dbfc24 100644
--- a/src/include/taler_signatures.h
+++ b/src/include/taler_signatures.h
@@ -504,11 +504,7 @@ struct TALER_MintKeySetPS
   struct GNUNET_TIME_AbsoluteNBO list_issue_date;
 
   /**
-   * Hash over the "inner" JSON with the key set.  FIXME: The use of
-   * JSON as what is being signed here is a bit of a hack, as the
-   * result depends on the JSON indentation and being canonical.
-   * We should consider using a more well-defined binary format to
-   * sign. (#3739)
+   * Hash over the various denomination signing keys returned.
    */
   struct GNUNET_HashCode hc;
 };
diff --git a/src/mint/taler-mint-httpd_test.c b/src/mint/taler-mint-httpd_test.c
index fbd24660f..6bf11c33e 100644
--- a/src/mint/taler-mint-httpd_test.c
+++ b/src/mint/taler-mint-httpd_test.c
@@ -79,12 +79,11 @@ TMH_TEST_handler_test_base32 (struct TMH_RequestHandler *rh,
 		      &hc);
   TMH_PARSE_release_data (spec);
   json_decref (json);
-  json = TALER_json_from_data (&hc, sizeof (struct GNUNET_HashCode));
-  res = TMH_RESPONSE_reply_json (connection,
-				 json,
-				 MHD_HTTP_OK);
-  json_decref (json);
-  return res;
+  return TMH_RESPONSE_reply_json_pack (connection,
+				       MHD_HTTP_OK,
+				       "{s:o}",
+				       "output",
+				       TALER_json_from_data (&hc, sizeof (struct GNUNET_HashCode)));
 }
 
 
@@ -160,11 +159,11 @@ TMH_TEST_handler_test_encrypt (struct TMH_RequestHandler *rh,
 			       spec[0].destination_size_out);
   GNUNET_free (out);
   TMH_PARSE_release_data (spec);
-  res = TMH_RESPONSE_reply_json (connection,
-				 json,
-				 MHD_HTTP_OK);
-  json_decref (json);
-  return res;
+  return TMH_RESPONSE_reply_json_pack (connection,
+				       MHD_HTTP_OK,
+				       "{s:o}",
+				       "output",
+				       json);
 }
 
 
@@ -221,12 +220,13 @@ TMH_TEST_handler_test_hkdf (struct TMH_RequestHandler *rh,
 		     spec[0].destination_size_out,
 		     NULL, 0);
   TMH_PARSE_release_data (spec);
-  json = TALER_json_from_data (&hc, sizeof (struct GNUNET_HashCode));
-  res = TMH_RESPONSE_reply_json (connection,
-				 json,
-				 MHD_HTTP_OK);
-  json_decref (json);
-  return res;
+  json = TALER_json_from_data (&hc,
+			       sizeof (struct GNUNET_HashCode));
+  return TMH_RESPONSE_reply_json_pack (connection,
+				       MHD_HTTP_OK,
+				       "{s:o}",
+				       "output",
+				       json);
 }