diff --git a/arff.py b/arff.py
index c8f8b34..9902035 100644
--- a/arff.py
+++ b/arff.py
@@ -625,17 +625,22 @@ def _encode_attribute(self, name, type_):
 
         return u'%s %s %s'%(_TK_ATTRIBUTE, name, type_)
 
-    def _encode_data(self, data):
+    def _encode_data(self, data, attributes):
         '''(INTERNAL) Encodes a line of data.
 
-        Data instances follow the csv format, i.e, attribute values are 
+        Data instances follow the csv format, i.e, attribute values are
         delimited by commas. After converted from csv.
 
         :param data: a list of values.
+        :param attributes: a list of attributes. Used to check if data is valid.
         :return: a string with the encoded data line.
         '''
+
+        if len(data) != len(attributes):
+            raise BadObject()
+
         new_data = []
-        for v in data:
+        for v, attr in zip(data, attributes):
             if v is None or v == u'':
                 s = '?'
             else:
@@ -701,12 +706,13 @@ def iter_encode(self, obj):
 
             yield self._encode_attribute(attr[0], attr[1])
         yield u''
+        attributes = obj['attributes']
 
         # DATA
         yield _TK_DATA
         if obj.get('data'):
             for inst in obj['data']:
-                yield self._encode_data(inst)
+                yield self._encode_data(inst, attributes)
 
         # FILLER
         yield self._encode_comment()
diff --git a/tests/test_encode_data.py b/tests/test_encode_data.py
index 3dcdad8..bfa4c0c 100644
--- a/tests/test_encode_data.py
+++ b/tests/test_encode_data.py
@@ -1,26 +1,35 @@
 import unittest
 import arff
 
+
 class TestEncodeData(unittest.TestCase):
-    def get_encoder(self):
-        decoder = arff.ArffEncoder()
-        return decoder
+    def setUp(self):
+        self.attributes = [('a1', 'INTEGER'), ('a2', 'INTEGER'),
+                           ('a3', 'STRING'), ('a4', 'STRING')]
+        self.encoder = arff.ArffEncoder()
+
 
     def test_simple(self):
-        encoder = self.get_encoder()
+        encoder = self.encoder
 
         fixture = [1, 3, 'Renato', 'Name with spaces']
-        result = encoder._encode_data(fixture)
+        result = encoder._encode_data(fixture, self.attributes)
         expected = u"1,3,Renato,'Name with spaces'"
 
         self.assertEqual(result, expected)
 
     def test_null_value(self):
-        encoder = self.get_encoder()
+        encoder = self.encoder
 
         fixture = [1, None, 'Renato', '']
-        result = encoder._encode_data(fixture)
+        result = encoder._encode_data(fixture, self.attributes)
         expected = u"1,?,Renato,?"
 
         self.assertEqual(result, expected)
 
+    def test_too_short(self):
+        encoder = self.encoder
+
+        fixture = [1, None]
+        self.assertRaises(arff.BadObject, encoder._encode_data, fixture,
+                          self.attributes)
\ No newline at end of file