diff --git a/AUTHORS.rst b/AUTHORS.rst
index 078ed993..6bbddfde 100644
--- a/AUTHORS.rst
+++ b/AUTHORS.rst
@@ -120,3 +120,4 @@ Patches and Suggestions
 - David Bonner <dbonner@gmail.com> @rascalking
 - Vinod Chandru
 - Johnny Goodnow <j.goodnow29@gmail.com>
+- Denis Ryzhkov <denisr@denisr.com>
diff --git a/requests/models.py b/requests/models.py
index c983db02..fe85a833 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -323,6 +323,7 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
         """Prepares the given HTTP headers."""
 
         if headers:
+            headers = dict((name.encode('ascii'), value) for name, value in headers.items())
             self.headers = CaseInsensitiveDict(headers)
         else:
             self.headers = CaseInsensitiveDict()
diff --git a/test_requests.py b/test_requests.py
index 6c4c3dd2..e12722d1 100644
--- a/test_requests.py
+++ b/test_requests.py
@@ -251,6 +251,9 @@ class RequestsTestCase(unittest.TestCase):
         requests.get(url, params={'foo': 'foo'})
         requests.get(httpbin('ø'), params={'foo': 'foo'})
 
+    def test_unicode_header_name(self):
+        requests.put(httpbin('put'), headers={str('Content-Type'): 'application/octet-stream'}, data='\xff') # compat.str is unicode.
+
     def test_urlencoded_get_query_multivalued_param(self):
 
         r = requests.get(httpbin('get'), params=dict(test=['foo', 'baz']))