diff --git a/ext/cvcircle32f.cpp b/ext/cvcircle32f.cpp
index 68a754e..ed44f09 100644
--- a/ext/cvcircle32f.cpp
+++ b/ext/cvcircle32f.cpp
@@ -42,8 +42,7 @@ define_ruby_class()
   rb_define_alloc_func(rb_klass, rb_allocate);
   rb_define_method(rb_klass, "center", RUBY_METHOD_FUNC(rb_center), 0);
   rb_define_method(rb_klass, "radius", RUBY_METHOD_FUNC(rb_radius), 0);
-
-  //rb_define_method(rb_klass, "to_s", RUBY_METHOD_FUNC(rb_to_s), 0);
+  rb_define_method(rb_klass, "[]", RUBY_METHOD_FUNC(rb_aref), 1);
   rb_define_method(rb_klass, "to_ary", RUBY_METHOD_FUNC(rb_to_ary), 0);
   rb_define_alias(rb_klass, "to_a", "to_ary");
 }
@@ -73,6 +72,32 @@ rb_radius(VALUE self)
   return rb_float_new(CVCIRCLE32F(self)->radius);
 }
 
+/*
+ * call-seq:
+ *   [<i>index</i>]
+ *
+ * Return value of <i>index</i> dimension.
+ */
+VALUE
+rb_aref(VALUE self, VALUE index)
+{
+  switch (NUM2INT(index)) {
+  case 0:
+    return DBL2NUM(CVCIRCLE32F(self)->center.x);
+    break;
+  case 1:
+    return DBL2NUM(CVCIRCLE32F(self)->center.y);
+    break;
+  case 2:
+    return DBL2NUM(CVCIRCLE32F(self)->radius);
+    break;
+  default:
+    rb_raise(rb_eIndexError, "index should be 0...3");
+    break;
+  }
+  return Qnil;
+}
+
 VALUE
 rb_to_ary(VALUE self)
 {
diff --git a/ext/cvcircle32f.h b/ext/cvcircle32f.h
index cccfa36..d2bd141 100644
--- a/ext/cvcircle32f.h
+++ b/ext/cvcircle32f.h
@@ -32,8 +32,7 @@ VALUE rb_allocate(VALUE klass);
 VALUE rb_initialize(int argc, VALUE *argv, VALUE self);
 VALUE rb_center(VALUE self);
 VALUE rb_radius(VALUE self);
-
-VALUE rb_to_s(VALUE self);
+VALUE rb_aref(VALUE self, VALUE index);
 VALUE rb_to_ary(VALUE self);
 
 VALUE new_object(CvCircle32f circle32f);
diff --git a/ext/cvmat.cpp b/ext/cvmat.cpp
index 3b6539a..80ed23f 100644
--- a/ext/cvmat.cpp
+++ b/ext/cvmat.cpp
@@ -4491,7 +4491,7 @@ rb_hough_circles_gradient(int argc, VALUE *argv, VALUE self)
 {
   SUPPORT_8UC1_ONLY(self);
   VALUE dp, min_dist, threshold_canny, threshold_accumulate, min_radius, max_radius, storage;
-  rb_scan_args(argc, argv, "24", &dp, &min_dist, &threshold_canny, &threshold_accumulate, &min_radius, &max_radius);
+  rb_scan_args(argc, argv, "42", &dp, &min_dist, &threshold_canny, &threshold_accumulate, &min_radius, &max_radius);
   storage = cCvMemStorage::new_object();
   CvSeq *seq = cvHoughCircles(CVARR(self), CVMEMSTORAGE(storage),
 			      CV_HOUGH_GRADIENT, NUM2DBL(dp), NUM2DBL(min_dist),
diff --git a/test/test_cvcircle32f.rb b/test/test_cvcircle32f.rb
new file mode 100755
index 0000000..786cfde
--- /dev/null
+++ b/test/test_cvcircle32f.rb
@@ -0,0 +1,41 @@
+#!/usr/bin/env ruby
+# -*- mode: ruby; coding: utf-8-unix -*- 
+require 'test/unit'
+require 'opencv'
+require File.expand_path(File.dirname(__FILE__)) + '/helper'
+
+include OpenCV
+
+# Tests for OpenCV::CvCircle32f
+class TestCvCircle32f < OpenCVTestCase
+  def setup
+    @circle = CvCircle32f.new
+  end
+  
+  def test_initialize
+    assert_equal(CvCircle32f, @circle.class)
+  end
+
+  def test_center
+    assert_equal(CvPoint2D32f, @circle.center.class)
+  end
+
+  def test_radius
+    assert_equal(Float, @circle.radius.class)
+  end
+
+  def test_aref
+    assert_equal(Float, @circle[0].class)
+    assert_equal(Float, @circle[1].class)
+    assert_equal(Float, @circle[2].class)
+    assert_raise(IndexError) {
+      @circle[3]
+    }
+  end
+
+  def test_to_ary
+    assert_equal(Array, @circle.to_ary.class)
+    assert_equal(2, @circle.to_ary.size)
+  end
+end
+
diff --git a/test/test_cvmat_imageprocessing.rb b/test/test_cvmat_imageprocessing.rb
index 525f5bf..bce5106 100755
--- a/test/test_cvmat_imageprocessing.rb
+++ b/test/test_cvmat_imageprocessing.rb
@@ -1370,5 +1370,26 @@ class TestCvMat_imageprocessing < OpenCVTestCase
     # }
     # snap mat0
   end
+
+  def test_hough_circles_gradient
+    mat0 = CvMat.load(FILENAME_LINES, CV_LOAD_IMAGE_ANYCOLOR | CV_LOAD_IMAGE_ANYDEPTH)
+    # make a binary image
+    mat = CvMat.new(mat0.rows, mat0.cols, :cv8u, 1)
+    (mat0.rows * mat0.cols).times { |i|
+      mat[i] = (mat0[i][0] <= 100) ? CvScalar.new(0) : CvScalar.new(255);
+    }
+
+    [mat.hough_circles_gradient(1.5, 40, 100, 50, 10, 50),
+     mat.hough_circles_gradient(1.5, 40, 100, 50)].each { |seq|
+      assert_equal(2, seq.size)
+    }
+
+    # Uncomment the following lines to show the result
+    # seq = mat.hough_circles_gradient(1.5, 40, 100, 50, 10, 50)
+    # seq.each { |circle|
+    #   mat0.circle!(circle.center, circle.radius, :color => CvColor::Red, :thickness => 2)
+    # }
+    # snap mat0
+  end
 end