diff --git a/subst.c b/subst.c

--- a/subst.c

+++ b/subst.c

@@ -7959,7 +7959,7 @@ parameter_brace_transform (varname, value, ind, xform, rtype, quoted, pflags, fl

       return ((char *)NULL);

     }

-  if (valid_parameter_transform (xform) == 0)

+  if (xform[0] == 0 || valid_parameter_transform (xform) == 0)

     {

       this_command_name = oname;

 #if 0 /* TAG: bash-5.2 Martin Schulte <gnu@schrader-schulte.de> 10/2020 */