diff --git a/nix-format.el b/nix-format.el
index db58002..8e6649b 100644
--- a/nix-format.el
+++ b/nix-format.el
@@ -16,23 +16,28 @@
 (defun nix--replace-buffer-contents (src dst)
   (if (fboundp 'replace-buffer-contents)
       (with-current-buffer dst (replace-buffer-contents src))
-    (unless  (string= (with-current-buffer src (buffer-string))
-		      (with-current-buffer dst (buffer-string)))
+    (unless (string= (with-current-buffer src (buffer-string))
+                     (with-current-buffer dst (buffer-string)))
       (with-current-buffer src
-	(copy-to-buffer dst (point-min) (point-max))))))
+        (copy-to-buffer dst (point-min) (point-max))))))
 
 (defun nix--format-call (buf nixfmt-bin)
-  "Format BUF using nixfmt."
-  (with-current-buffer (get-buffer-create "*nixfmt*")
-    (erase-buffer)
-    (insert-buffer-substring buf)
-    (if (zerop (call-process-region (point-min) (point-max) nixfmt-bin t t nil))
-	(nix--replace-buffer-contents (current-buffer) buf)
-      (error "Nixfmt failed, see *nixfmt* buffer for details"))))
+  "Format BUF using program NIXFMT-BIN."
+  (let ((temp-file (make-nearby-temp-file "nixfmt")))
+    (unwind-protect
+        (let ((out-buf (get-buffer-create "*nixfmt*")))
+          (with-current-buffer out-buf
+            (erase-buffer))
+          (with-current-buffer buf
+            (write-region (point-min) (point-max) temp-file nil 'no-visit nil nil))
+          (if (zerop (process-file nixfmt-bin temp-file out-buf))
+              (nix--replace-buffer-contents out-buf buf)
+            (error "Nixfmt failed, see *nixfmt* buffer for details")))
+      (delete-file temp-file))))
 
 (defun nix--find-nixfmt ()
   "Find the nixfmt binary, or error if it's missing."
-  (let ((nixfmt-bin (executable-find nix-nixfmt-bin)))
+  (let ((nixfmt-bin (executable-find nix-nixfmt-bin t)))
     (unless nixfmt-bin
       (error "Could not locate executable %S" nix-nixfmt-bin))
     nixfmt-bin))