diff --git a/pkgs/racket-test-core/tests/racket/file.rktl b/pkgs/racket-test-core/tests/racket/file.rktl
index 9ef5b34a19..0226e35c37 100644
--- a/pkgs/racket-test-core/tests/racket/file.rktl
+++ b/pkgs/racket-test-core/tests/racket/file.rktl
@@ -454,7 +454,9 @@
   (close-output-port o))
 (test 900 file-size tempfilename)
 (let ([o (open-output-file tempfilename #:exists 'update)])
+  (file-position o 10)
   (file-truncate o 399)
+  (test 10 file-position o)
   (close-output-port o))
 (test 399 file-size tempfilename)
 
diff --git a/racket/src/rktio/rktio_file.c b/racket/src/rktio/rktio_file.c
index 35da8ac260..b7bd01dff4 100644
--- a/racket/src/rktio/rktio_file.c
+++ b/racket/src/rktio/rktio_file.c
@@ -360,7 +360,7 @@ rktio_ok_t rktio_set_file_size(rktio_t *rktio, rktio_fd_t *rfd, rktio_filesize_t
       } else {
 	if (SetEndOfFile((HANDLE)fd)) {
 	  /* we assume that this works: */
-	  (void)SetFilePointer((HANDLE)fd, lo_w, &hi_w, FILE_BEGIN);
+	  (void)SetFilePointer((HANDLE)fd, old_lo_w, &old_hi_w, FILE_BEGIN);
 	  return 1;
 	}
         get_windows_error();