diff --git a/tests/doctest.lisp b/tests/doctest.lisp
index 2a593a2..58a786e 100644
--- a/tests/doctest.lisp
+++ b/tests/doctest.lisp
@@ -105,10 +105,12 @@
 (define-test doctest-file ()
   (multiple-value-bind (file-failed file-passed)
       (uiop:with-temporary-file (:pathname test-file)
-        (with-open-file (stream test-file :direction :output)
-          (format stream (documentation doctest:test 'function))
-          (finish-output stream))
-        (doctest:test test-file))
+        (unwind-protect (progn
+                          (uiop:delete-file-if-exists test-file)
+                          (with-open-file (stream test-file :direction :output :external-format :utf-8)
+                            (write-string (documentation #'doctest:test 'function) stream))
+                          (doctest:test test-file))
+          (uiop:delete-file-if-exists test-file)))
    (multiple-value-bind (doctest-failed doctest-passed) (doctest:test #'doctest:test)
      (assert-eql doctest-failed file-failed)
      (assert-eql doctest-passed file-passed))))