diff --git a/test/readline/test_readline.rb b/test/readline/test_readline.rb
index fa933765bc..7ac2212719 100644
--- a/test/readline/test_readline.rb
+++ b/test/readline/test_readline.rb
@@ -527,6 +527,7 @@ module BasetestReadline
   end
 
   def test_using_quoting_detection_proc_with_multibyte_input
+    Readline.completion_append_character = nil
     saved_completer_quote_characters = Readline.completer_quote_characters
     saved_completer_word_break_characters = Readline.completer_word_break_characters