diff --git a/lib/chibi/memoize-test.sld b/lib/chibi/memoize-test.sld
index 14eb243a..b7ae94ec 100644
--- a/lib/chibi/memoize-test.sld
+++ b/lib/chibi/memoize-test.sld
@@ -1,6 +1,13 @@
 (define-library (chibi memoize-test)
   (export run-tests)
-  (import (scheme base) (scheme file) (chibi memoize) (chibi test))
+  (import (scheme base)
+          (scheme file)
+          (chibi filesystem)
+          (chibi memoize)
+          (chibi pathname)
+          (chibi process)
+          (chibi temp-file)
+          (chibi test))
   (begin
     (define (run-tests)
       (test-begin "memoize")
@@ -39,13 +46,44 @@
           (test 9 (f 3))
           (test 1 n)))
 
-      (letrec ((fib (lambda (n)
-                      (if (<= n 1)
-                          1
-                          (+ (fib (- n 1)) (fib (- n 2)))))))
-        (let ((f (memoize-to-file fib 'memo-dir: "/tmp/memo.d/")))
-          (test 89 (f 10))
-          (test-assert (file-exists? "/tmp/memo.d/10.memo"))
-          (test 89 (f 10))))
+      (let ((calls 0))
+        (letrec ((fib (lambda (n)
+                        (set! calls (+ calls 1))
+                        (if (<= n 1)
+                            1
+                            (+ (fib (- n 1)) (fib (- n 2)))))))
+         (call-with-temp-dir
+          "memo.d"
+          (lambda (dir preserve)
+            (let ((f (memoize-to-file fib 'memo-dir: dir)))
+              (test 89 (f 10))
+              (test 177 calls)
+              ;; (test-assert (file-exists? (make-path dir "%2810%29.memo")))
+              (test 89 (f 10))
+              (test 177 calls))))))
+
+      (call-with-temp-file
+       "tmp-file"
+       (lambda (tmp-file out preserve)
+         (write-string "123" out)
+         (close-output-port out)
+         (let ((calls 0))
+           (let ((fast-file-size
+                 (memoize-file-loader
+                  (lambda (file)
+                    (set! calls (+ calls 1))
+                    (file-size file)))))
+             (test 3 (fast-file-size tmp-file))
+             (test 1 calls)
+             (test 3 (fast-file-size tmp-file))
+             (test 1 calls)
+             (sleep 1)
+             (call-with-output-file tmp-file
+               (lambda (out) (write-string "1234" out)))
+             (test 4 (fast-file-size tmp-file))
+             (test 2 calls)
+             (test 4 (fast-file-size tmp-file))
+             (test 2 calls)
+             ))))
 
       (test-end))))