diff --git a/ChangeLog b/ChangeLog
index aea3500cb5..837062f7d0 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Aug 19 13:59:43 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* compar.c (rb_cmperr): preserve encodings of arguments in the
+	  message.
+
 Tue Aug 19 10:13:23 2014  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* ext/thread/thread.c (get_array): check instance variables are
diff --git a/compar.c b/compar.c
index 893cde79fc..a38668edf1 100644
--- a/compar.c
+++ b/compar.c
@@ -18,17 +18,16 @@ static ID cmp;
 void
 rb_cmperr(VALUE x, VALUE y)
 {
-    const char *classname;
+    VALUE classname;
 
     if (SPECIAL_CONST_P(y)) {
-	y = rb_inspect(y);
-	classname = StringValuePtr(y);
+	classname = rb_inspect(y);
     }
     else {
-	classname = rb_obj_classname(y);
+	classname = rb_class_path(rb_obj_class(y));
     }
-    rb_raise(rb_eArgError, "comparison of %s with %s failed",
-	     rb_obj_classname(x), classname);
+    rb_raise(rb_eArgError, "comparison of %"PRIsVALUE" with %"PRIsVALUE" failed",
+	     rb_class_path(rb_obj_class(x)), classname);
 }
 
 static VALUE
diff --git a/test/ruby/test_comparable.rb b/test/ruby/test_comparable.rb
index 05426af139..1c3cbeaf1a 100644
--- a/test/ruby/test_comparable.rb
+++ b/test/ruby/test_comparable.rb
@@ -73,6 +73,10 @@ class TestComparable < Test::Unit::TestCase
   def test_err
     assert_raise(ArgumentError) { 1.0 < nil }
     assert_raise(ArgumentError) { 1.0 < Object.new }
+    e = Module.new {break module_eval("class E\u{30a8 30e9 30fc}; self; end")}
+    assert_raise_with_message(ArgumentError, /E\u{30a8 30e9 30fc}/) {
+      1.0 < e.new
+    }
   end
 
   def test_inversed_compare