diff --git a/ext/opencv/size.cpp b/ext/opencv/size.cpp
index 9fb834e..8d5b189 100644
--- a/ext/opencv/size.cpp
+++ b/ext/opencv/size.cpp
@@ -1,4 +1,5 @@
 // -*- mode: c++; coding: utf-8 -*-
+#include <sstream>
 #include "ruby.h"
 #include "opencv2/core.hpp"
 
@@ -99,11 +100,34 @@ namespace rubyopencv {
 	selfptr->width = NUM2INT(v1);
 	selfptr->height = NUM2INT(v2);
 	break;
+      default:
+	rb_raise(rb_eArgError, "wrong number of arguments (%d for 0 or 2)", argc);
+	break;
       }
 
       return self;
     }
 
+    /*
+     * Return size as an +String+.
+     *
+     * @overload to_s
+     * @return [String] String representation of the size
+     */
+    VALUE rb_to_s(VALUE self) {
+      std::stringstream s;
+      cv::Size* selfptr = obj2size(self);
+      s << *selfptr;
+
+      VALUE param[3];
+      param[0] = rb_str_new2("#<%s:%s>");
+      param[1] = rb_str_new2(rb_class2name(CLASS_OF(self)));
+      param[2] = rb_str_new2(s.str().c_str());
+
+      int n = sizeof(param) / sizeof(param[0]);
+      return rb_f_sprintf(n, param);
+    }
+
     void init() {
       VALUE opencv = rb_define_module("OpenCV");
 
@@ -115,6 +139,8 @@ namespace rubyopencv {
       rb_define_method(rb_klass, "width=", RUBY_METHOD_FUNC(rb_set_width), 1);
       rb_define_method(rb_klass, "height", RUBY_METHOD_FUNC(rb_height), 0);
       rb_define_method(rb_klass, "height=", RUBY_METHOD_FUNC(rb_set_height), 1);
+
+      rb_define_method(rb_klass, "to_s", RUBY_METHOD_FUNC(rb_to_s), 0);
     }
   }
 }
diff --git a/test/test_size.rb b/test/test_size.rb
new file mode 100755
index 0000000..f60943d
--- /dev/null
+++ b/test/test_size.rb
@@ -0,0 +1,54 @@
+#!/usr/bin/env ruby
+# -*- mode: ruby; coding: utf-8 -*-
+require 'test/unit'
+require 'opencv'
+require File.expand_path(File.dirname(__FILE__)) + '/helper'
+
+include OpenCV
+
+# Tests for OpenCV::Size
+class TestSize < OpenCVTestCase
+  def test_width
+    size = Size.new
+    size.width = 100
+    assert_equal(100, size.width)
+    size.width = 200
+    assert_equal(200, size.width)
+  end
+
+  def test_height
+    size = Size.new
+    size.height = 100
+    assert_equal(100, size.height)
+    size.height = 200
+    assert_equal(200, size.height)
+  end
+
+  def test_initialize
+    size = Size.new
+    assert_equal(0, size.width)
+    assert_equal(0, size.height)
+
+    size = Size.new(10, 20)
+    assert_equal(10, size.width)
+    assert_equal(20, size.height)
+
+    assert_raise(TypeError) {
+      Size.new(DUMMY_OBJ, 1)
+    }
+    assert_raise(TypeError) {
+      Size.new(1, DUMMY_OBJ)
+    }
+    assert_raise(ArgumentError) {
+      Size.new(1)
+    }
+    assert_raise(ArgumentError) {
+      Size.new(1, 2, 3)
+    }
+  end
+
+  def test_to_s
+    size = Size.new(10, 20)
+    assert_equal('#<OpenCV::Size:[10 x 20]>', size.to_s)
+  end
+end