diff --git a/Lib/test/test_urllib2.py b/Lib/test/test_urllib2.py
index c0366dd..ef59cfa 100644
--- a/Lib/test/test_urllib2.py
+++ b/Lib/test/test_urllib2.py
@@ -1209,6 +1209,7 @@
         self.get.add_data("spam")
         self.assertTrue(self.get.has_data())
         self.assertEqual("POST", self.get.get_method())
+        self.assertRaises(TypeError,self.get.add_data, "more spam")
 
     def test_get_full_url(self):
         self.assertEqual("http://www.python.org/~jeremy/",
diff --git a/Lib/urllib2.py b/Lib/urllib2.py
index 122f777..8b26971 100644
--- a/Lib/urllib2.py
+++ b/Lib/urllib2.py
@@ -226,6 +226,9 @@
     # XXX these helper methods are lame
 
     def add_data(self, data):
+        if self.has_data():
+            raise TypeError("Request Obj already contains data: %s" %
+                            self.data)
         self.data = data
 
     def has_data(self):