diff --git a/sendgrid/transport/smtp.py b/sendgrid/transport/smtp.py
index 82a084d4f..0b08ef565 100644
--- a/sendgrid/transport/smtp.py
+++ b/sendgrid/transport/smtp.py
@@ -180,9 +180,9 @@ def _getFileMIME(self, attach):
             msg.set_payload(data)
             encoders.encode_base64(msg)
 
-        msg.add_header('Content-Disposition', 'attachment', filename=filename)
-        
         if attach.get('cid', False):
-          msg.add_header('Content-ID', '<%s>' % attach['cid'])
+            msg.add_header('Content-ID', '<%s>' % attach['cid'])
+        else:
+            msg.add_header('Content-Disposition', 'attachment', filename=filename)
 
         return msg
\ No newline at end of file
diff --git a/test/test_smtp_transport.py b/test/test_smtp_transport.py
index ae950690c..acac34911 100644
--- a/test/test_smtp_transport.py
+++ b/test/test_smtp_transport.py
@@ -48,12 +48,15 @@ def test_smtp_transport_content_id_header(self):
 
         f = smtp_transport._getFileMIME({'file': 'img.png', 'name': 'contents'})
         self.assertEqual(None, f.get('Content-ID'))
+        self.assertEqual('attachment; filename="contents"', f.get('Content-Disposition'))
 
         f = smtp_transport._getFileMIME({'file': 'img.png', 'name': 'contents', 'cid': None})
         self.assertEqual(None, f.get('Content-ID'))
+        self.assertEqual('attachment; filename="contents"', f.get('Content-Disposition'))
 
         f = smtp_transport._getFileMIME({'file': 'img.png', 'name': 'contents', 'cid': 'cid'})
         self.assertEqual('<cid>', f.get('Content-ID'))
+        self.assertEqual(None, f.get('Content-Disposition'))
 
 
 class FakeException(IOError):