diff --git a/nbconvert.py b/nbconvert.py
index 2fac471..e4802fe 100755
--- a/nbconvert.py
+++ b/nbconvert.py
@@ -109,13 +109,13 @@ class Converter(object):
 class ConverterRST(Converter):
     extension = 'rst'
     figures_counter = 0
+    heading_level = {1: '=', 2: '-', 3: '`', 4: '\'', 5: '.', 6: '~'}
 
     def render_heading(self, cell):
         """convert a heading cell to rst
 
         Returns list."""
-        heading_level = {1: '=', 2: '-', 3: '`', 4: '\'', 5: '.', 6: '~'}
-        marker = heading_level[cell.level]
+        marker = self.heading_level[cell.level]
         return ['{0}\n{1}\n'.format(cell.source, marker * len(cell.source))]
 
     def render_code(self, cell):
diff --git a/tests/test_simple.py b/tests/test_simple.py
index 7ee2485..eeb6577 100644
--- a/tests/test_simple.py
+++ b/tests/test_simple.py
@@ -55,9 +55,8 @@ def test_render_heading():
         nt.assert_true(isinstance(rst_list, list))  # render should return a list
         rst_str = "".join(rst_list)
         # Confirm rst content
-        heading_level = {1: '=', 2: '-', 3: '`', 4: '\'', 5: '.', 6: '~'}
         chk_str = "Test for heading type H{0}\n{1}\n".format(
-             level, heading_level[level] * 24)
+             level, c.heading_level[level] * 24)
         nt.assert_equal(rst_str, chk_str)