Index: exp_ch3.adb
===================================================================
--- exp_ch3.adb	(revision 213322)
+++ exp_ch3.adb	(working copy)
@@ -3763,8 +3763,16 @@
                if Has_Invariants (Etype (Id))
                  and then In_Open_Scopes (Scope (R_Type))
                then
-                  Append_To (Stmts, Build_Component_Invariant_Call (Id));
+                  if Has_Unchecked_Union (R_Type) then
+                     Error_Msg_NE
+                       ("invariants cannot be checked on components of "
+                         & "unchecked_union type&?", Decl, R_Type);
+                     return Empty_List;
 
+                  else
+                     Append_To (Stmts, Build_Component_Invariant_Call (Id));
+                  end if;
+
                elsif Is_Access_Type (Etype (Id))
                  and then not Is_Access_Constant (Etype (Id))
                  and then Has_Invariants (Designated_Type (Etype (Id)))