GNAT Error?

["Jeffrey R.Carter" <spam.jrcarter.not@spam.acm.org.not>]

I have this code:

package Alloc_Err is
    type RT is record
       F1 : Integer;
       F2 : Integer;
    end record;

    type Grid is array (Positive range <>, Positive range <>) of RT with
       Dynamic_Predicate => Grid'First (1) = 1 and Grid'First (2) = 1;

    procedure What;
end Alloc_Err;

package Alloc_Err is
    type RT is record
       F1 : Integer;
       F2 : Integer;
    end record;

    type Grid is array (Positive range <>, Positive range <>) of RT with
       Dynamic_Predicate => Grid'First (1) = 1 and Grid'First (2) = 1;

    procedure What;
end Alloc_Err;

and GNAT 12.3.0 and 13.2.0 say

alloc_err.adb:5:26: error: invalid use of subtype mark in expression or call

This doesn't happen if the Dynamic_Predicate is removed. This looks like an 
error to me, but I thought I'd better see if there's something I've missed.

-- 
Jeff Carter
"I like it when the support group complains that they have
insufficient data on mean time to repair bugs in Ada software."
Robert I. Eachus
91