diff --git a/src/filo.ads b/src/filo.ads
index 6a9a4b8..6c21c8c 100644
--- a/src/filo.ads
+++ b/src/filo.ads
@@ -4,7 +4,7 @@
 
 package FILO is
 
-   type Blockdev_Length is range 0 .. Interfaces.Unsigned_64'Last;
+   type Blockdev_Length is range 0 .. Interfaces.Integer_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;