diff --git a/src/filo-fs.adb b/src/filo-fs.adb
index 69ed2ad..91f86f0 100644
--- a/src/filo-fs.adb
+++ b/src/filo-fs.adb
@@ -20,8 +20,8 @@
 
    function Part_Len return Partition_Length
    is
-     (Partition_Length (unsigned_long'Min (
-        C_Part_Length, unsigned_long (Partition_Length'Last))));
+     (Partition_Length (Unsigned_64'Min (
+        Unsigned_64 (C_Part_Length), Unsigned_64 (Partition_Length'Last))));
 
    function File_Max return File_Length is
    begin