diff --git a/src/blockdev.c b/src/blockdev.c
index 2395c45..91879c4 100644
--- a/src/blockdev.c
+++ b/src/blockdev.c
@@ -32,7 +32,7 @@
 	}
 
 	part_start = 0;
-	part_length = device_size;
+	part_length = device_size / 512;
 
 	return 1;
 }
@@ -79,13 +79,13 @@
 {
 	if (start + size <= device_size) {
 		part_start = start;
-		part_length = size;
+		part_length = size / 512;
 	}
 }
 
 void dev_get_partition(unsigned long *start, unsigned long *size)
 {
 	*start = part_start;
-	*size = part_length;
+	*size = part_length * 512;
 }
 
diff --git a/src/filo-fs.adb b/src/filo-fs.adb
index 91f86f0..bc4c246 100644
--- a/src/filo-fs.adb
+++ b/src/filo-fs.adb
@@ -18,10 +18,19 @@
       Convention     => C,
       External_Name  => "filepos";
 
+   pragma Warnings
+     (GNAT, Off, "condition can only be False*",
+      Reason => "Depends on `unsigned long` size.");
+   pragma Warnings
+     (GNAT, Off, "condition is always True",
+      Reason => "Depends on `unsigned long` size.");
    function Part_Len return Partition_Length
    is
-     (Partition_Length (Unsigned_64'Min (
-        Unsigned_64 (C_Part_Length), Unsigned_64 (Partition_Length'Last))));
+     (if Unsigned_64 (C_Part_Length) <= Unsigned_64 (Partition_Length'Last) / 512
+      then Partition_Length (C_Part_Length) * 512
+      else Partition_Length'Last);
+   pragma Warnings (GNAT, On, "condition can only be False*");
+   pragma Warnings (GNAT, On, "condition is always True");
 
    function File_Max return File_Length is
    begin