diff --git a/releng/README.releng b/releng/README.releng
index 90d1ecf7..90cfe743 100644
--- a/releng/README.releng
+++ b/releng/README.releng
@@ -15,6 +15,7 @@ http://www.gnu.org/software/xorriso/
  + file name starts with releng_
  + mandatory options -rc [-clean]
  + well documented configuration file test.conf{.template}
+ + throw FAIL string to stdout if any failure is detected
  + exit code 0 on success, non-zero on failure
 
 * TESTS LIST
diff --git a/releng/releng_build_isojigdo b/releng/releng_build_isojigdo
index 2402fa50..3584a60f 100755
--- a/releng/releng_build_isojigdo
+++ b/releng/releng_build_isojigdo
@@ -160,7 +160,7 @@ case ${DIFF_RET} in
       echo -e "$0: diff ${IMG}.iso ${IMG}.new matched.\n"
      ;;
      *)
-      echo -e "$0: ATTN: diff returned code: $DIFF_RET\n"
+      echo -e "$0: FAIL: diff returned code: $DIFF_RET\n"
      ;;
 esac