diff --git a/Modules/readline.c b/Modules/readline.c
index 2d75ace8577..6850b016bda 100644
--- a/Modules/readline.c
+++ b/Modules/readline.c
@@ -573,6 +573,7 @@ setup_readline(void)
 	rl_completer_word_break_characters =
 		strdup(" \t\n`~!@#$%^&*()-=+[{]}\\|;:'\",<>/?");
 		/* All nonalphanums except '.' */
+	rl_completion_append_character ='\0';
 
 	begidx = PyInt_FromLong(0L);
 	endidx = PyInt_FromLong(0L);