diff --git a/CHANGES.rst b/CHANGES.rst
index e32e3368d90..1c5f5685150 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -28,6 +28,8 @@ Changes
 - Connection can be destroyed before response get processed if
   `await aiohttp.request(..)` is used #1981
 
+- MultipartReader doesn't work with -OO #1969
+
 
 2.1.0 (2017-05-26)
 ------------------
diff --git a/aiohttp/multipart.py b/aiohttp/multipart.py
index 83201f21134..4f94845f7cb 100644
--- a/aiohttp/multipart.py
+++ b/aiohttp/multipart.py
@@ -282,7 +282,8 @@ def read_chunk(self, size=chunk_size):
         if self._read_bytes == self._length:
             self._at_eof = True
         if self._at_eof:
-            assert b'\r\n' == (yield from self._content.readline()), \
+            clrf = yield from self._content.readline()
+            assert b'\r\n' == clrf, \
                 'reader did not read all the data or it is malformed'
         return chunk