diff --git a/ChangeLog b/ChangeLog
index aa809e4074..8a74d01e01 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Mon Nov 22 11:58:11 2010  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* string.c (rb_str_concat): set ENC_CODERANGE_VALID when the
+	  receiver is 7BIT and the argument is non ASCII.
+
 Mon Nov 22 01:48:58 2010  Tadayoshi Funaba  <tadf@dotrb.org>
 
 	* lib/date.rb: some improvements for performance.
diff --git a/string.c b/string.c
index f77032f635..20466e16f2 100644
--- a/string.c
+++ b/string.c
@@ -2043,6 +2043,8 @@ rb_str_concat(VALUE str1, VALUE str2)
 	}
 	rb_str_resize(str1, pos+len);
 	rb_enc_mbcput(lc, RSTRING_PTR(str1)+pos, enc);
+	if (cr == ENC_CODERANGE_7BIT && lc > 127)
+	    cr = ENC_CODERANGE_VALID;
 	ENC_CODERANGE_SET(str1, cr);
 	return str1;
     }
diff --git a/test/ruby/test_m17n.rb b/test/ruby/test_m17n.rb
index 863f047ad8..7713f07df2 100644
--- a/test/ruby/test_m17n.rb
+++ b/test/ruby/test_m17n.rb
@@ -1102,6 +1102,7 @@ class TestM17N < Test::Unit::TestCase
   end
 
   def test_str_concat
+    assert_equal(1, "".concat(0xA2))
     assert_equal("A\x84\x31\xA4\x39".force_encoding("GB18030"),
                  "A".force_encoding("GB18030") << 0x8431A439)
   end