diff -r 2072deff3b2f Lib/email/message.py
--- a/Lib/email/message.py	Mon Feb 24 14:31:25 2014 -0800
+++ b/Lib/email/message.py	Mon Mar 03 00:49:48 2014 +0530
@@ -203,7 +203,10 @@
         if self._payload is None:
             self._payload = [payload]
         else:
-            self._payload.append(payload)
+            try:
+                self._payload.append(payload)
+            except AttributeError:
+                raise TypeError("Attach not valid on a message with a non-multipart payload")
 
     def get_payload(self, i=None, decode=False):
         """Return a reference to the payload.
diff -r 2072deff3b2f Lib/test/test_email/test_email.py
--- a/Lib/test/test_email/test_email.py	Mon Feb 24 14:31:25 2014 -0800
+++ b/Lib/test/test_email/test_email.py	Mon Mar 03 00:49:48 2014 +0530
@@ -124,6 +124,13 @@
         msg.set_payload([])
         self.assertEqual(msg.get_payload(), [])
 
+    def test_email_attach_to_string(self):
+        msg = Message()
+        msg['Content-Type'] = 'multipart/mixed'
+        msg.set_payload('string payload')
+        sub_msg = MIMEMessage(Message())
+        self.assertRaisesRegexp(TypeError,"Attach not valid on a message with a non-multipart payload",msg.attach,sub_msg)
+
     def test_get_charsets(self):
         eq = self.assertEqual