diff --git a/lib/bson/types/object_id.rb b/lib/bson/types/object_id.rb
index 7b97699..3567118 100644
--- a/lib/bson/types/object_id.rb
+++ b/lib/bson/types/object_id.rb
@@ -131,11 +131,7 @@ module BSON
     #
     # @return [String]
     def to_s
-      str = ' ' * 24
-      12.times do |i|
-        str[i * 2, 2] = '%02x' % @data[i]
-      end
-      str
+      @data.map {|e| v=e.to_s(16); v.size == 1 ? "0#{v}" : v }.join
     end
 
     def inspect
diff --git a/test/bson/object_id_test.rb b/test/bson/object_id_test.rb
index 01e076a..9f533d4 100644
--- a/test/bson/object_id_test.rb
+++ b/test/bson/object_id_test.rb
@@ -51,6 +51,12 @@ class ObjectIdTest < Test::Unit::TestCase
     assert_equal 24, $1.length
   end
 
+  def test_to_s2
+    @o = ObjectId.new([76, 244, 52, 174, 44, 84, 121, 76, 88, 0, 0, 3])
+    s = '4cf434ae2c54794c58000003'
+    assert_equal @o.to_s, s
+  end
+
   def test_method
     assert_equal ObjectId.from_string(@o.to_s), BSON::ObjectId(@o.to_s)
   end