diff --git a/aiohttp/client_reqrep.py b/aiohttp/client_reqrep.py
index 8c70592f4c5..5ee57674830 100644
--- a/aiohttp/client_reqrep.py
+++ b/aiohttp/client_reqrep.py
@@ -745,13 +745,14 @@ def json(self, *, encoding=None, loads=json.loads):
             client_logger.warning(
                 'Attempt to decode JSON with unexpected mimetype: %s', ctype)
 
-        if not self._content.strip():
+        stripped = self._content.strip()
+        if not stripped:
             return None
 
         if encoding is None:
             encoding = self._get_encoding()
 
-        return loads(self._content.decode(encoding))
+        return loads(stripped.decode(encoding))
 
     if PY_35:
         @asyncio.coroutine