diff --git a/pysstv/sstv.py b/pysstv/sstv.py
index 5f8d6f3..496a953 100644
--- a/pysstv/sstv.py
+++ b/pysstv/sstv.py
@@ -83,7 +83,7 @@ class SSTV(object):
             freq_factor = freq * factor
             for sample in xrange(tx):
                 yield sin(sample * freq_factor + offset)
-            offset += sample * freq_factor
+            offset += (sample + 1) * freq_factor
             samples -= tx
 
     def gen_freq_bits(self):
diff --git a/pysstv/tests/test_sstv.py b/pysstv/tests/test_sstv.py
index 022f135..ffcd630 100644
--- a/pysstv/tests/test_sstv.py
+++ b/pysstv/tests/test_sstv.py
@@ -69,7 +69,7 @@ class TestSSTV(unittest.TestCase):
         mock_open = MagicMock(return_value=sio)
         with mock.patch('__builtin__.open', mock_open):
             self.s.write_wav('unittest.wav')
-        expected = '8aa1d52b222b411e032ce2bce77d203a'
+        expected = 'dd7eed880ab3360fb79ce09c469deee2'
         data = sio.getvalue()
         actual = hashlib.md5(data).hexdigest()
         self.assertEqual(expected, actual)