diff --git a/file.scm b/file.scm
index 11b1bcc0..f61961d0 100644
--- a/file.scm
+++ b/file.scm
@@ -312,10 +312,10 @@ EOF
        (let ((tmp
               (or (get-environment-variable "TMPDIR")
                   (get-environment-variable "TEMP")
-                  (get-environment-variable "TMP")
-                  "/tmp")))
-         (set! temp tmp)
-         tmp)))
+                  (get-environment-variable "TMP"))))
+          (when tmp
+            (set! temp tmp))
+          (or tmp "/tmp"))))
   (set! create-temporary-file
     (lambda (#!optional (ext "tmp"))
       (##sys#check-string ext 'create-temporary-file)