diff --git a/src/filo-fs-ext2.ads b/src/filo-fs-ext2.ads
index bbf959b..6003198 100644
--- a/src/filo-fs-ext2.ads
+++ b/src/filo-fs-ext2.ads
@@ -71,7 +71,8 @@
    with
       Object_Size => (Inode_Extents_Index'Last + 1) * 8;
 
-   type Inode_Index is new Unsigned_32 range 2 .. Unsigned_32'Last;
+   type Inode_0_Index is new Unsigned_32;
+   subtype Inode_Index is Inode_0_Index range 2 .. Inode_0_Index'Last;
    subtype Inode_Size is Positive range 128 .. Positive (Unsigned_16'Last);
    subtype Desc_Size  is Positive range  32 .. 2 ** 15; -- power-of-2 that fits in 16 bits
 
@@ -86,12 +87,13 @@
       Inline      : Inode_Extents := (others => 16#00#);
    end record;
 
-   type Group_Index is new Natural range 0 .. Natural (Inode_Index'Last / 2);
+   type Group_Index is new Inode_0_Index;
    subtype Group_In_Block_Count is Group_Index
       range 1 .. Group_Index (Block_Size'Last / Desc_Size'First);
    type Desc_In_Block_Index is new Natural range 0 .. Natural (Group_In_Block_Count'Last - 1);
 
-   type Inode_In_Group_Index is new Natural range 0 .. Natural (Inode_Index'Last / 2);
+   subtype Inode_In_Group_Count is Inode_0_Index range 1 .. Inode_0_Index'Last;
+   type Inode_In_Group_Index is new Inode_0_Index range 0 .. Inode_In_Group_Count'Last - 1;
    subtype Inode_In_Block_Count is Inode_In_Group_Index
       range 1 .. Inode_In_Group_Index (Block_Size'Last / Inode_Size'First);
    type Inode_In_Block_Index is new Natural range 0 .. Natural (Inode_In_Block_Count'Last - 1);
@@ -101,7 +103,7 @@
       First_Data_Block     : Unsigned_32 := Unsigned_32'First;
       Block_Size_Bits      : Log_Block_Size := Log_Block_Size'First;
       Block_Size           : Ext2.Block_Size := Ext2.Block_Size'First;
-      Inodes_Per_Group     : Inode_Index := Inode_Index'First;
+      Inodes_Per_Group     : Inode_In_Group_Count := Inode_In_Group_Count'First;
       Inode_Size           : Ext2.Inode_Size := Ext2.Inode_Size'First;
       Inodes_Per_Block     : Inode_In_Block_Count := Inode_In_Block_Count'First;
       Desc_Size            : Ext2.Desc_Size := Ext2.Desc_Size'First;