diff --git a/ChangeLog b/ChangeLog
index 74469588e9..d739594a4d 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Apr  8 20:08:16 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* string.c (rb_str_rstrip_bang): should not sign-expand non-ascii.
+	  [ruby-core:23158]
+
 Wed Apr  8 17:29:29 2009  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* string.c (rb_str_chop_bang): reset coderange. [ruby-core:23155]
diff --git a/string.c b/string.c
index 2744ea94b3..2b790a082f 100644
--- a/string.c
+++ b/string.c
@@ -6197,7 +6197,8 @@ rb_str_rstrip_bang(VALUE str)
 
     /* remove trailing spaces or '\0's */
     if (single_byte_optimizable(str)) {
-	while (s < t && (*(t-1) == '\0' || rb_enc_isspace(*(t-1), enc))) t--;
+	unsigned char c;
+	while (s < t && ((c = *(t-1)) == '\0' || rb_enc_isspace(c, enc))) t--;
     }
     else {
 	char *tp;
diff --git a/test/ruby/test_string.rb b/test/ruby/test_string.rb
index b209296ef9..e87b6d3c8f 100644
--- a/test/ruby/test_string.rb
+++ b/test/ruby/test_string.rb
@@ -1139,6 +1139,8 @@ class TestString < Test::Unit::TestCase
   def test_strip
     assert_equal(S("x"), S("      x        ").strip)
     assert_equal(S("x"), S(" \n\r\t     x  \t\r\n\n      ").strip)
+    assert_equal(S(""), S("\xa0".force_encoding("iso-8859-1")).strip)
+    assert_equal(S("a"), S("a\xa0".force_encoding("iso-8859-1")).strip)
   end
 
   def test_strip!