access aliased obstacle

[tmoran@bix.com]

To pass a data structure to an OS routine I tried

  type elements(discriminant: enumeration_type:=normal_value) is record
    case discriminant is
    ...
  end record;
  for elements'size use 64;  -- size does not vary

  type list_of_elements is array(1 .. 17) of aliased elements;

but one of my Ada 95 compilers objected to aliasing unless I make a
subtype with a specific discriminant value, which defeats the purpose.
The LRM appears to me to agree with this compiler.  The only obvious
possibility is unchecked_conversion.  What is the 'right' way?