diff --git a/requests/models.py b/requests/models.py
index 75692447..c0d613bb 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -348,7 +348,7 @@ class Request(object):
             else:
                 fn = guess_filename(v) or k
                 fp = v
-            if isinstance(fp, bytes):
+            if isinstance(fp, (bytes, str)):
                 fp = StringIO(fp)
             fields.update({k: (fn, fp.read())})
 
diff --git a/tests/test_requests.py b/tests/test_requests.py
index 43745a56..e8a9d4ee 100755
--- a/tests/test_requests.py
+++ b/tests/test_requests.py
@@ -344,6 +344,15 @@ class RequestsTestSuite(TestSetup, TestBaseMixin, unittest.TestCase):
             post3 = post(url, files={'fname.txt': 'fdata', 'fname2.txt':open(__file__,'rb')})
             self.assertEqual(post3.status_code, 200)
 
+            post4 = post(url, files={'fname.txt': u'fdata'})
+            self.assertEqual(post4.status_code, 200)
+
+            post5 = post(url, files={'file': ('file.txt', 'more fdata')})
+            self.assertEqual(post5.status_code, 200)
+
+            post6 = post(url, files={'fname.txt': u'\xe9'})
+            self.assertEqual(post6.status_code, 200)
+
     def test_nonzero_evaluation(self):
 
         for service in SERVICES: