diff --git a/functional-tests/disk-units.scm b/functional-tests/disk-units.scm
new file mode 100644
index 0000000..fb75d32
--- /dev/null
+++ b/functional-tests/disk-units.scm
@@ -0,0 +1,6 @@
+(library
+  (disk-units)
+  (export meg)
+  (import (rnrs))
+
+  (define (meg n) (* 1024 1024 n)))
diff --git a/functional-tests/thin-functional-tests.scm b/functional-tests/thin-functional-tests.scm
index 913356b..9dded40 100644
--- a/functional-tests/thin-functional-tests.scm
+++ b/functional-tests/thin-functional-tests.scm
@@ -5,6 +5,7 @@
 
   (import
     (chezscheme)
+    (disk-units)
     (fmt fmt)
     (functional-tests)
     (process)
@@ -20,10 +21,6 @@
   (define-tool thin-restore)
   (define-tool thin-rmap)
 
-  ;; FIXME: start a disk units library
-  (define (meg n)
-    (* 1024 1024 n))
-
   (define-syntax with-thin-xml
     (syntax-rules ()
       ((_ (v) b1 b2 ...)