diff --git a/tests/test_io.py b/tests/test_io.py
index c1350b03a..5216728b2 100644
--- a/tests/test_io.py
+++ b/tests/test_io.py
@@ -16,7 +16,7 @@ class TestInputOutput(unittest.TestCase):
         rel_fnames = ["non_existent_file.txt"]
         addable_rel_fnames = []
         commands = None
-        autocompleter = AutoCompleter(root, rel_fnames, addable_rel_fnames, commands)
+        autocompleter = AutoCompleter(root, rel_fnames, addable_rel_fnames, commands, "utf-8")
         self.assertEqual(autocompleter.words, set(rel_fnames))