diff --git a/aiohttp/client.py b/aiohttp/client.py
index d95cce18e2d..61d84116198 100644
--- a/aiohttp/client.py
+++ b/aiohttp/client.py
@@ -9,6 +9,7 @@
 import weakref
 import warnings
 import chardet
+from os import fstat
 
 import aiohttp
 from . import hdrs, helpers, streams
@@ -383,7 +384,13 @@ def update_body_from_data(self, data):
             assert not isinstance(data, io.StringIO), \
                 'attempt to send text data instead of binary'
             self.body = data
-            self.chunked = True
+            if not self.chunked and isinstance(data, io.BufferedReader):
+                # Not chunking if content-length can be determined
+                size = fstat(data.fileno()).st_size - data.tell()
+                self.headers[hdrs.CONTENT_LENGTH] = str(size)
+                self.chunked = False
+            else:
+                self.chunked = True
             if hasattr(data, 'mode'):
                 if data.mode == 'r':
                     raise ValueError('file {!r} should be open in binary mode'
diff --git a/tests/test_client.py b/tests/test_client.py
index 5f40db3f122..9250b9e23bc 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -7,6 +7,7 @@
 import unittest
 import unittest.mock
 import urllib.parse
+import os.path
 
 import aiohttp
 from aiohttp.client import ClientRequest, ClientResponse
@@ -542,6 +543,39 @@ def test_chunked_length(self):
         self.assertEqual(req.headers['TRANSFER-ENCODING'], 'chunked')
         self.assertNotIn('CONTENT-LENGTH', req.headers)
 
+    def test_file_upload_not_chunked(self):
+        here = os.path.dirname(__file__)
+        fname = os.path.join(here, 'sample.key')
+        with open(fname, 'rb') as f:
+            req = ClientRequest(
+                'post', 'http://python.org/',
+                data=f)
+            self.assertFalse(req.chunked)
+            self.assertEqual(req.headers['CONTENT-LENGTH'],
+                             str(os.path.getsize(fname)))
+
+    def test_file_upload_not_chunked_seek(self):
+        here = os.path.dirname(__file__)
+        fname = os.path.join(here, 'sample.key')
+        with open(fname, 'rb') as f:
+            f.seek(100)
+            req = ClientRequest(
+                'post', 'http://python.org/',
+                data=f)
+            self.assertEqual(req.headers['CONTENT-LENGTH'],
+                             str(os.path.getsize(fname) - 100))
+
+    def test_file_upload_force_chunked(self):
+        here = os.path.dirname(__file__)
+        fname = os.path.join(here, 'sample.key')
+        with open(fname, 'rb') as f:
+            req = ClientRequest(
+                'post', 'http://python.org/',
+                data=f,
+                chunked=True)
+            self.assertTrue(req.chunked)
+            self.assertNotIn('CONTENT-LENGTH', req.headers)
+
     def test_expect100(self):
         req = ClientRequest('get', 'http://python.org/',
                             expect100=True, loop=self.loop)