diff --git a/src/filo.ads b/src/filo.ads
index c0a7e3d..93985b1 100644
--- a/src/filo.ads
+++ b/src/filo.ads
@@ -4,8 +4,10 @@
 
 package FILO is
 
-   type Partition_Length is range 0 .. Interfaces.Unsigned_64'Last;
-   subtype Partition_Offset is Partition_Length range 0 .. Partition_Length'Last - 1;
+   type Blockdev_Length is range 0 .. Interfaces.Unsigned_64'Last;
+   subtype Blockdev_Offset is Blockdev_Length range 0 .. Blockdev_Length'Last - 1;
+   subtype Partition_Length is Blockdev_Length;
+   subtype Partition_Offset is Blockdev_Offset;
 
    BLOCK_SIZE : constant := 512;
    type Block_Offset is range 0 .. Partition_Offset'Last / BLOCK_SIZE;