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