diff --git a/gcc/ada/checks.adb b/gcc/ada/checks.adb
--- a/gcc/ada/checks.adb
+++ b/gcc/ada/checks.adb
@@ -5094,7 +5094,8 @@ package body Checks is
         --  Don't deal with enumerated types with non-standard representation
 
         or else (Is_Enumeration_Type (Typ)
-                   and then Present (Enum_Pos_To_Rep (Base_Type (Typ))))
+                   and then Present (Enum_Pos_To_Rep
+                                       (Implementation_Base_Type (Typ))))
 
         --  Ignore type for which an error has been posted, since range in
         --  this case may well be a bogosity deriving from the error. Also


diff --git a/gcc/ada/exp_attr.adb b/gcc/ada/exp_attr.adb
--- a/gcc/ada/exp_attr.adb
+++ b/gcc/ada/exp_attr.adb
@@ -7103,7 +7103,10 @@ package body Exp_Attr is
       --  See separate sections below for the generated code in each case.
 
       when Attribute_Valid => Valid : declare
-         PBtyp : Entity_Id := Base_Type (Validated_View (Ptyp));
+         PBtyp : Entity_Id := Implementation_Base_Type (Validated_View (Ptyp));
+         pragma Assert (Is_Scalar_Type (PBtyp)
+                          or else Serious_Errors_Detected > 0);
+
          --  The scalar base type, looking through private types
 
          Save_Validity_Checks_On : constant Boolean := Validity_Checks_On;