diff --git a/converters/base.py b/converters/base.py
index 5691dd3..3233f68 100755
--- a/converters/base.py
+++ b/converters/base.py
@@ -72,7 +72,7 @@ class Converter(object):
     files_dir = str()
     with_preamble = True
     user_preamble = None
-    output = str()
+    output = unicode()
     raw_as_verbatim = False
     
     def __init__(self, infile):
@@ -140,6 +140,7 @@ class Converter(object):
         if not hasattr(self, 'nb'):
             self.read()
         self.output = self.convert()
+        assert(type(self.output) == unicode)
         return self.save()
 
     def read(self):
diff --git a/converters/notebook.py b/converters/notebook.py
index 541b0c0..cc4f0c9 100755
--- a/converters/notebook.py
+++ b/converters/notebook.py
@@ -1,4 +1,5 @@
 from converters.base import Converter
+from converters.utils import cell_to_lines
 from shutil import rmtree
 import json
 
@@ -23,7 +24,7 @@ class ConverterNotebook(Converter):
         rmtree(self.files_dir)
 
     def convert(self):
-        return json.dumps(json.loads(Converter.convert(self, ',')), indent=1, sort_keys=True)
+        return unicode(json.dumps(json.loads(Converter.convert(self, ',')), indent=1, sort_keys=True))
 
     def optional_header(self):
         s = \
diff --git a/converters/utils.py b/converters/utils.py
index e36cfc5..5109461 100755
--- a/converters/utils.py
+++ b/converters/utils.py
@@ -1,8 +1,14 @@
 from __future__ import print_function
 from lexers import IPythonLexer
+
 import subprocess
+import copy
+import json
 import re
+
 from IPython.utils.text import indent
+from IPython.utils import path, py3compat
+from IPython.nbformat.v3.nbjson import BytesEncoder
 
 #-----------------------------------------------------------------------------
 # Utility functions