diff --git a/requests/models.py b/requests/models.py
index 43a297e6..81bd1a84 100644
--- a/requests/models.py
+++ b/requests/models.py
@@ -434,7 +434,7 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
             if files:
                 raise NotImplementedError('Streamed bodies and files are mutually exclusive.')
 
-            if length is not None:
+            if length:
                 self.headers['Content-Length'] = builtin_str(length)
             else:
                 self.headers['Transfer-Encoding'] = 'chunked'
@@ -446,8 +446,6 @@ class PreparedRequest(RequestEncodingMixin, RequestHooksMixin):
                 if data:
                     body = self._encode_params(data)
                     if isinstance(data, basestring) or hasattr(data, 'read'):
-                        if hasattr(data, 'fileno') and length == 0:
-                            self.headers['Transfer-Encoding'] = 'chunked'
                         content_type = None
                     else:
                         content_type = 'application/x-www-form-urlencoded'