diff --git a/src/filo-fs-iso9660.ads b/src/filo-fs-iso9660.ads
index 0a28cc2..480ce39 100644
--- a/src/filo-fs-iso9660.ads
+++ b/src/filo-fs-iso9660.ads
@@ -49,22 +49,31 @@
    type State is (Unmounted, Mounted, File_Opened);
 
    FSBlock_Size : constant := 2048;
+   subtype FSBlock_Length is Index_Type range 0 .. FSBlock_Size;
    subtype FSBlock_Index is Index_Type range 0 .. FSBlock_Size - 1;
 
    type FSBlock_Count is range 0 .. 2 ** 32 - 1;
    subtype FSBlock is FSBlock_Count range 0 .. FSBlock_Count'Last - 1;
    type FSBlock_Logical is new FSBlock;
 
+   type FS_Record is record
+      Block    : FSBlock := 0;
+      Offset   : FSBlock_Length := 0;
+      Size     : FSBlock_Length := 0;
+   end record
+   with
+      Dynamic_Predicate =>
+         Size <= FSBlock_Size - Offset;
+
    subtype Directory_Record_Range is Index_Type range 0 .. 32;
    subtype Directory_Record is Buffer_Type (Directory_Record_Range);
    subtype Directory_Record_Offset is FSBlock_Index
       range 0 .. FSBlock_Size - Directory_Record'Length;
 
    -- We'll use the absolute position of the dir record
-   type Inode_Index is record
-      Block : FSBlock := 0;
-      Offset : Directory_Record_Offset := 0;
-   end record;
+   subtype Inode_Index is FS_Record
+   with
+      Dynamic_Predicate => Inode_Index.Offset <= Directory_Record_Offset'Last;
    type Inode_Length is range 0 .. FSBlock_Count'Last * FSBlock_Size;
 
    type Mount_State is record