diff --git a/ext/readline/readline.c b/ext/readline/readline.c
index 6100633f20..87a1ff0371 100644
--- a/ext/readline/readline.c
+++ b/ext/readline/readline.c
@@ -602,15 +602,14 @@ static VALUE
 readline_s_get_completion_append_character(VALUE self)
 {
 #ifdef HAVE_RL_COMPLETION_APPEND_CHARACTER
-    VALUE str;
+    char buf[1];
 
     rb_secure(4);
     if (rl_completion_append_character == '\0')
 	return Qnil;
 
-    str = rb_str_new(0, 1);
-    RSTRING_PTR(str)[0] = rl_completion_append_character;
-    return str;
+    buf[0] = (char) rl_completion_append_character;
+    return rb_locale_str_new(buf, 1);
 #else
     rb_notimplement();
     return Qnil; /* not reached */
diff --git a/test/readline/test_readline.rb b/test/readline/test_readline.rb
index 36aadd92d7..cf809e20d7 100644
--- a/test/readline/test_readline.rb
+++ b/test/readline/test_readline.rb
@@ -166,12 +166,18 @@ class TestReadline < Test::Unit::TestCase
 
   def test_completion_append_character
     begin
-      Readline.completion_append_character = "x"
-      assert_equal("x", Readline.completion_append_character)
-      Readline.completion_append_character = "xyz"
-      assert_equal("x", Readline.completion_append_character)
-      Readline.completion_append_character = nil
-      assert_equal(nil, Readline.completion_append_character)
+      enc = Encoding.default_internal || Encoding.find("locale")
+      data_expected = [
+                       ["x", "x"],
+                       ["xyx", "x"],
+                       [" ", " "],
+                       ["\t", "\t"],
+                      ]
+      data_expected.each do |(data, expected)|
+        Readline.completion_append_character = data
+        assert_equal(expected, Readline.completion_append_character)
+        assert_equal(enc, Readline.completion_append_character.encoding)
+      end
       Readline.completion_append_character = ""
       assert_equal(nil, Readline.completion_append_character)
     rescue NotImplementedError