diff --git a/requests/models.py b/requests/models.py
index 5fe570e2..29c06c6b 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -330,9 +330,10 @@ class Request(object):
             result = []
             for k, vs in to_key_val_list(data):
                 for v in isinstance(vs, list) and vs or [vs]:
-                    result.append(
-                        (k.encode('utf-8') if isinstance(k, str) else k,
-                         v.encode('utf-8') if isinstance(v, str) else v))
+                    if v is not None:
+                        result.append(
+                            (k.encode('utf-8') if isinstance(k, str) else k,
+                             v.encode('utf-8') if isinstance(v, str) else v))
             return urlencode(result, doseq=True)
         else:
             return data
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 0dba704a..8e2ebf18 100755
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -1112,5 +1112,15 @@ class RequestsTestSuite(TestSetup, TestBaseMixin, unittest.TestCase):
         Requests.exceptions.InvalidURL instead of UnicodeError."""
         self.assertRaises(InvalidURL, get, 'http://.google.com/')
 
+    def test_none_vals_in_data_are_deleted(self):
+        """Test that keys with None as the value are removed instead of
+        being posted."""
+        data = {'key1': 'value1', 'key2': None}
+        r = post(httpbin('post'), data=data)
+        vals = r.json['form']
+        self.assertEqual(vals['key1'], 'value1')
+        # The 'key2' key should not have been sent.
+        self.assertTrue(vals.get('key2') is None)
+
 if __name__ == '__main__':
     unittest.main()