diff --git a/functional-tests/cache-functional-tests.scm b/functional-tests/cache-functional-tests.scm
index a0271f2..60ca1c0 100644
--- a/functional-tests/cache-functional-tests.scm
+++ b/functional-tests/cache-functional-tests.scm
@@ -19,13 +19,13 @@
   (define-syntax with-cache-xml
     (syntax-rules ()
       ((_ (v) b1 b2 ...)
-       (with-temp-file-containing ((v (fmt #f (generate-xml 512 1024 128))))
+       (with-temp-file-containing ((v "cache.xml" (fmt #f (generate-xml 512 1024 128))))
          b1 b2 ...))))
 
   (define-syntax with-valid-metadata
     (syntax-rules ()
       ((_ (md) b1 b2 ...)
-       (with-temp-file-sized ((md (meg 4)))
+       (with-temp-file-sized ((md "cache.bin" (meg 4)))
          (with-cache-xml (xml)
            (cache-restore "-i" xml "-o" md)
            b1 b2 ...)))))
@@ -34,13 +34,13 @@
   (define-syntax with-corrupt-metadata
     (syntax-rules ()
       ((_ (md) b1 b2 ...)
-       (with-temp-file-sized ((md (meg 4)))
+       (with-temp-file-sized ((md "cache.bin" (meg 4)))
          b1 b2 ...))))
 
   (define-syntax with-empty-metadata
     (syntax-rules ()
       ((_ (md) b1 b2 ...)
-       (with-temp-file-sized ((md (meg 4)))
+       (with-temp-file-sized ((md "cache.bin" (meg 4)))
                             b1 b2 ...))))
 
   ;; We have to export something that forces all the initialisation expressions
@@ -177,7 +177,7 @@
 
    (define-scenario (cache-restore tiny-output-file)
                     "Fails if the output file is too small."
-                    (with-temp-file-sized ((md (* 1024 4)))
+                    (with-temp-file-sized ((md "cache.bin" (* 1024 4)))
                       (with-cache-xml (xml)
                         (receive (_ stderr) (run-fail "cache_restore" "-i" xml "-o" md)
                           (assert-starts-with cache-restore-outfile-too-small-text stderr)))))
@@ -250,7 +250,7 @@
                     "cache_dump followed by cache_restore is a noop."
                     (with-valid-metadata (md)
                       (receive (d1-stdout _) (cache-dump md)
-                        (with-temp-file-containing ((xml d1-stdout))
+                        (with-temp-file-containing ((xml "cache.xml" d1-stdout))
                           (cache-restore "-i" xml "-o" md)
                           (receive (d2-stdout _) (cache-dump md)
                             (assert-equal d1-stdout d2-stdout))))))
diff --git a/functional-tests/process.scm b/functional-tests/process.scm
index b7b788e..884b703 100644
--- a/functional-tests/process.scm
+++ b/functional-tests/process.scm
@@ -28,7 +28,8 @@
     (apply fmt #f (map dsp (intersperse " " cmd-and-args))))
 
   (define (run . cmd-and-args)
-    (with-temp-file (stdout-file stderr-file)
+    (with-temp-file ((stdout-file "stdout")
+                     (stderr-file "stderr"))
       (let* ((short-cmd (build-command-line cmd-and-args))
              (cmd (fmt #f (dsp (build-command-line cmd-and-args))
                        (dsp " > ")
diff --git a/functional-tests/temp-file.scm b/functional-tests/temp-file.scm
index 407e5a6..bef5254 100644
--- a/functional-tests/temp-file.scm
+++ b/functional-tests/temp-file.scm
@@ -14,7 +14,9 @@
     disable-unlink)
 
   (import (chezscheme)
-          (fmt fmt))
+          (fmt fmt)
+          (srfi s8 receive)
+          (only (srfi s1 lists) span))
 
   ;; FIXME: global var!  Not thread safe.
   (define working-dir "/tmp")
@@ -40,38 +42,41 @@
                       (auto-unlink-file path
                                    (thunk)))))
 
-   (define temp-filename
-     (let ((counter 0))
-      (lambda ()
-        (let loop ()
-         (let ((path (fmt #f (cat (dsp working-dir) (dsp "/tmp-")
-                                  (pad-char #\0 (pad/left 4 (num counter)))))))
-           (set! counter (+ counter 1))
-           (if (file-exists? path)
-               (loop)
-               path))))))
+  (define temp-filename
+    (lambda (filename)
+      (let ((counter 0))
+       (let loop ()
+        (let ((path (fmt #f (cat (dsp working-dir)
+                                 (dsp "/")
+                                 (pad-char #\0 (pad/left 4 (num counter)))
+                                 (dsp "-")
+                                 (dsp filename)))))
+          (set! counter (+ counter 1))
+          (if (file-exists? path)
+              (loop)
+              path))))))
 
    ;; fn takes the path
-   (define (with-temp-file-thunk fn)
-     (let ((path (temp-filename)))
+   (define (with-temp-file-thunk filename fn)
+     (let ((path (temp-filename filename)))
       (auto-unlink-file path
         (lambda () (fn path)))))
 
    (define-syntax with-temp-file
      (syntax-rules ()
-       ((_ (v) b1 b2 ...)
-        (with-temp-file-thunk
+       ((_ ((v f)) b1 b2 ...)
+        (with-temp-file-thunk f
           (lambda (v)
             b1 b2 ...)))
 
-       ((_ (v1 v2 ...) b1 b2 ...)
-        (with-temp-file-thunk
+       ((_ ((v1 f1) v2 ...) b1 b2 ...)
+        (with-temp-file-thunk f1
           (lambda (v1)
             (with-temp-file (v2 ...) b1 b2 ...))))))
 
    ;; Creates a temporary file with the specified contents.
-   (define (with-temp-file-containing-thunk contents fn)
-     (with-temp-file-thunk
+   (define (with-temp-file-containing-thunk filename contents fn)
+     (with-temp-file-thunk filename
        (lambda (path)
          (with-output-to-file path (lambda ()
                                      (put-string (current-output-port) contents)))
@@ -79,18 +84,18 @@
 
    (define-syntax with-temp-file-containing
      (syntax-rules ()
-       ((_ ((v txt)) b1 b2 ...)
-        (with-temp-file-containing-thunk
+       ((_ ((v f txt)) b1 b2 ...)
+        (with-temp-file-containing-thunk f
           txt (lambda (v) b1 b2 ...)))
 
-       ((_ ((v txt) rest ...) b1 b2 ...)
-        (with-temp-file-containing-thunk
-          txt (lambda (v txt)
+       ((_ ((v f txt) rest ...) b1 b2 ...)
+        (with-temp-file-containing-thunk f
+          txt (lambda (v)
                 (with-temp-file-containing (rest ...)
                                            b1 b2 ...))))))
 
-   (define (with-temp-file-sized-thunk size fn)
-     (with-temp-file-thunk
+   (define (with-temp-file-sized-thunk filename size fn)
+     (with-temp-file-thunk filename
        (lambda (path)
          (let ((cmd (fmt #f (dsp "fallocate -l ") (wrt size) (dsp " ") (dsp path))))
           (system cmd)
@@ -98,14 +103,14 @@
 
    (define-syntax with-temp-file-sized
      (syntax-rules ()
-       ((_ ((v size)) b1 b2 ...)
-        (with-temp-file-sized-thunk
+       ((_ ((v f size)) b1 b2 ...)
+        (with-temp-file-sized-thunk f
           size
           (lambda (v)
             b1 b2 ...)))
 
-       ((_ ((v size) rest ...) b1 b2 ...)
-        (with-temp-file-sized-thunk
+       ((_ ((v f size) rest ...) b1 b2 ...)
+        (with-temp-file-sized-thunk f
           size (lambda (v)
                  (with-temp-file-sized (rest ...) b1 b2 ...))))))
 
diff --git a/functional-tests/thin-functional-tests.scm b/functional-tests/thin-functional-tests.scm
index 54b1dbd..75c76f4 100644
--- a/functional-tests/thin-functional-tests.scm
+++ b/functional-tests/thin-functional-tests.scm
@@ -24,13 +24,13 @@
   (define-syntax with-thin-xml
     (syntax-rules ()
       ((_ (v) b1 b2 ...)
-       (with-temp-file-containing ((v (fmt #f (generate-xml 10 1000))))
+       (with-temp-file-containing ((v "thin.xml" (fmt #f (generate-xml 10 1000))))
                                   b1 b2 ...))))
 
   (define-syntax with-valid-metadata
     (syntax-rules ()
       ((_ (md) b1 b2 ...)
-       (with-temp-file-sized ((md (meg 4)))
+       (with-temp-file-sized ((md "thin.bin" (meg 4)))
          (with-thin-xml (xml)
            (thin-restore "-i" xml "-o" md)
            b1 b2 ...)))))
@@ -39,7 +39,7 @@
   (define-syntax with-corrupt-metadata
     (syntax-rules ()
       ((_ (md) b1 b2 ...)
-       (with-temp-file-sized ((md (meg 4)))
+       (with-temp-file-sized ((md "thin.bin" (meg 4)))
          b1 b2 ...))))
 
   ;; We have to export something that forces all the initialisation expressions
@@ -132,13 +132,13 @@
 
    (define-scenario (thin-restore no-input-file)
                     "forget to specify an input file"
-                    (with-temp-file-sized ((md (meg 4)))
+                    (with-temp-file-sized ((md "thin.bin" (meg 4)))
                       (receive (_ stderr) (run-fail "thin_restore" "-o" md)
                         (assert-starts-with "No input file provided." stderr))))
 
    (define-scenario (thin-restore missing-input-file)
                     "the input file can't be found"
-                    (with-temp-file-sized ((md (meg 4)))
+                    (with-temp-file-sized ((md "thin.bin" (meg 4)))
                       (receive (_ stderr) (run-fail "thin_restore -i no-such-file -o" md)
                         (assert-starts-with "Couldn't stat file" stderr))))
 
@@ -150,21 +150,21 @@
 
    (define-scenario (thin-restore tiny-output-file)
                     "Fails if the output file is too small."
-                    (with-temp-file-sized ((md (* 1024 4)))
+                    (with-temp-file-sized ((md "thin.bin" (* 1024 4)))
                       (with-thin-xml (xml)
                         (receive (_ stderr) (run-fail "thin_restore" "-i" xml "-o" md)
                           (assert-starts-with thin-restore-outfile-too-small-text stderr)))))
 
    (define-scenario (thin-restore q)
                     "thin_restore accepts -q"
-                    (with-temp-file-sized ((md (meg 4)))
+                    (with-temp-file-sized ((md "thin.bin" (meg 4)))
                       (with-thin-xml (xml)
                         (receive (stdout _) (thin-restore "-i" xml "-o" md "-q")
                           (assert-eof stdout)))))
 
    (define-scenario (thin-restore quiet)
                     "thin_restore accepts --quiet"
-                    (with-temp-file-sized ((md (meg 4)))
+                    (with-temp-file-sized ((md "thin.bin" (meg 4)))
                       (with-thin-xml (xml)
                         (receive (stdout _) (thin-restore "-i" xml "-o" md "--quiet")
                           (assert-eof stdout)))))
@@ -173,7 +173,7 @@
                     "thin_dump followed by thin_restore is a noop."
                     (with-valid-metadata (md)
                       (receive (d1-stdout _) (thin-dump md)
-                        (with-temp-file-containing ((xml d1-stdout))
+                        (with-temp-file-containing ((xml "thin.xml" d1-stdout))
                           (thin-restore "-i" xml "-o" md)
                           (receive (d2-stdout _) (thin-dump md)
                             (assert-equal d1-stdout d2-stdout))))))