diff --git a/tornado/iostream.py b/tornado/iostream.py
index <HASH>..<HASH> 100644
--- a/tornado/iostream.py
+++ b/tornado/iostream.py
@@ -67,7 +67,7 @@ class BaseIOStream(object):
     def __init__(self, io_loop=None, max_buffer_size=None,
                  read_chunk_size=4096):
         self.io_loop = io_loop or ioloop.IOLoop.current()
-        self.max_buffer_size = 104857600 or max_buffer_size
+        self.max_buffer_size = max_buffer_size or 104857600
         self.read_chunk_size = read_chunk_size
         self.error = None
         self._read_buffer = collections.deque()
Corrected or logic to make use of max_buffer_size if it is setted