diff --git a/IPython/nbconvert/writers/files.py b/IPython/nbconvert/writers/files.py
index 35aca20..1e3e7d2 100644
--- a/IPython/nbconvert/writers/files.py
+++ b/IPython/nbconvert/writers/files.py
@@ -1,17 +1,7 @@
-"""
-Contains writer for writing nbconvert output to filesystem.
-"""
-#-----------------------------------------------------------------------------
-#Copyright (c) 2013, the IPython Development Team.
-#
-#Distributed under the terms of the Modified BSD License.
-#
-#The full license is in the file COPYING.txt, distributed with this software.
-#-----------------------------------------------------------------------------
+"""Contains writer for writing nbconvert output to filesystem."""
 
-#-----------------------------------------------------------------------------
-# Imports
-#-----------------------------------------------------------------------------
+# Copyright (c) IPython Development Team.
+# Distributed under the terms of the Modified BSD License.
 
 import io
 import os
@@ -19,6 +9,7 @@ import glob
 
 from IPython.utils.traitlets import Unicode
 from IPython.utils.path import link_or_copy
+from IPython.utils.py3compat import unicode_type
 
 from .base import WriterBase
 
@@ -110,6 +101,11 @@ class FilesWriter(WriterBase):
 
             # Write conversion results.
             self.log.info("Writing %i bytes to %s", len(output), dest)
-            with io.open(dest, 'w', encoding='utf-8') as f:
-                f.write(output)
+            if isinstance(output, unicode_type):
+                with io.open(dest, 'w', encoding='utf-8') as f:
+                    f.write(output)
+            else:
+                with io.open(dest, 'wb') as f:
+                    f.write(output)
+                
             return dest