diff --git a/ChangeLog b/ChangeLog
index a8d6391b8e..092731df02 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Wed Aug 31 16:28:04 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* test/ruby/test_io_m17n.rb (TestIO_M17N#test_{default_mode_on_dosish,
+	  default_mode_on_unix,text_mode,binary_mode}): tests for [Bug #5164].
+
 Wed Aug 31 15:54:11 2011  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* ext/json: Merge json gem v1.5.4 (3dab4c5a6a97fac03dac).
diff --git a/test/ruby/test_io_m17n.rb b/test/ruby/test_io_m17n.rb
index 091b04a5af..01dca47f7f 100644
--- a/test/ruby/test_io_m17n.rb
+++ b/test/ruby/test_io_m17n.rb
@@ -2069,5 +2069,32 @@ EOT
     }
     assert(c.ascii_only?, "should be ascii_only #{bug4557}")
   end
-end
 
+  def test_default_mode_on_dosish
+    with_tmpdir {
+      open("a", "w") {|f| f.puts}
+      assert_equal("\r\n", IO.binread("a"))
+    }
+  end if /mswin|mingw/ =~ RUBY_PLATFORM
+
+  def test_default_mode_on_unix
+    with_tmpdir {
+      open("a", "w") {|f| f.puts}
+      assert_equal("\n", IO.binread("a"))
+    }
+  end unless /mswin|mingw/ =~ RUBY_PLATFORM
+
+  def test_text_mode
+    with_tmpdir {
+      open("a", "wt") {|f| f.puts}
+      assert_equal("\r\n", IO.binread("a"))
+    }
+  end
+
+  def test_binary_mode
+    with_tmpdir {
+      open("a", "wb") {|f| f.puts}
+      assert_equal("\n", IO.binread("a"))
+    }
+  end
+end