diff --git a/ext/cvmat.cpp b/ext/cvmat.cpp
index 30b4db7..f7286c3 100644
--- a/ext/cvmat.cpp
+++ b/ext/cvmat.cpp
@@ -1380,14 +1380,16 @@ rb_repeat(VALUE self, VALUE object)
 
 /*
  * call-seq:
- *   flip(:x) -> cvmat
- *   flip(:y) -> cvmat
- *   flip ->  -> cvmat
+ *   flip(:x)  -> cvmat
+ *   flip(:y)  -> cvmat
+ *   flip(:xy) -> cvmat
+ *   flip      -> cvmat
  *
  * Return new flipped 2D array.
- * * flip(:x) - flip around horizontal
- * * flip(:y) - flip around vertical
- * * flip - flip around both axises
+ * * flip(:x)  - flip around horizontal
+ * * flip(:y)  - flip around vertical
+ * * flip(:xy) - flip around both axises
+ * * flip      - flip around vertical
  */
 VALUE
 rb_flip(int argc, VALUE *argv, VALUE self)
@@ -1397,9 +1399,10 @@ rb_flip(int argc, VALUE *argv, VALUE self)
 
 /*
  * call-seq:
- *   flip!(:x) -> self
- *   flip!(:y) -> self
- *   flip!     -> self
+ *   flip!(:x)  -> self
+ *   flip!(:y)  -> self
+ *   flip!(:xy) -> self
+ *   flip!      -> self
  *
  * Flip 2D array. Return self.
  *
@@ -1409,14 +1412,16 @@ VALUE
 rb_flip_bang(int argc, VALUE *argv, VALUE self)
 {
   VALUE format;
-  int mode = -1;
+  int mode = 0;
   if (rb_scan_args(argc, argv, "01", &format) > 0) {
     if (rb_to_id(format) == rb_intern("x"))
       mode = 1;
     else if (rb_to_id(format) == rb_intern("y"))
       mode = 0;
+    else if (rb_to_id(format) == rb_intern("xy"))
+      mode = -1;
     else
-      rb_warn("argument may be :x or :y");        
+      rb_warn("argument may be :x or :y or :xy");
   }
   cvFlip(CVARR(self), NULL, mode);
   return self;
diff --git a/test/test_cvmat.rb b/test/test_cvmat.rb
index dc50b66..91274f8 100755
--- a/test/test_cvmat.rb
+++ b/test/test_cvmat.rb
@@ -604,6 +604,42 @@ class TestCvMat < OpenCVTestCase
       }
     }
   end
+
+  def test_flip
+    m0 = create_cvmat(2, 3)
+
+    m1 = m0.clone
+    m1.flip!(:x)
+    m2 = m0.clone.flip(:x)
+    m3 = m0.clone
+    m3.flip!(:y)
+    m4 = m0.clone.flip(:y)
+    m5 = m0.clone
+    m5.flip!(:xy)
+    m6 = m0.clone.flip(:xy)
+    m7 = m0.clone
+    m7.flip!
+    m8 = m0.clone.flip
+
+    [m1, m2, m3, m4, m5, m6, m7, m8].each { |m|
+      assert_equal(m0.height, m.height)
+      assert_equal(m0.width, m.width)
+    }
+    m0.height.times { |j|
+      m0.width.times { |i|
+        ri = m0.width - i - 1
+        rj = m0.height - j - 1
+        assert_cvscalar_equal(m0[ri, j], m1[i, j])
+        assert_cvscalar_equal(m0[ri, j], m2[i, j])
+        assert_cvscalar_equal(m0[i, rj], m3[i, j])
+        assert_cvscalar_equal(m0[i, rj], m4[i, j])
+        assert_cvscalar_equal(m0[ri, rj], m5[i, j])
+        assert_cvscalar_equal(m0[ri, rj], m6[i, j])
+        assert_cvscalar_equal(m0[i, rj], m7[i, j])
+        assert_cvscalar_equal(m0[i, rj], m8[i, j])
+      }
+    }
+  end
   
   # def test_avg_sdv
   #   m = CvMat.new(1, 8, CV_32F)