diff --git a/pynfe/utils/__init__.py b/pynfe/utils/__init__.py
index 2aeeab6..9a62c18 100644
--- a/pynfe/utils/__init__.py
+++ b/pynfe/utils/__init__.py
@@ -16,6 +16,13 @@ try:
 except ImportError:
     raise Exception('Falhou ao importar flags')
 
+try:
+    basestring
+    unicode
+except NameError:
+    basestring = str
+    unicode = str
+
 
 # @memoize
 def so_numeros(texto):