diff --git a/graphene/types/scalars.py b/graphene/types/scalars.py
index 86380b68..a5596d28 100644
--- a/graphene/types/scalars.py
+++ b/graphene/types/scalars.py
@@ -1,3 +1,4 @@
+import six
 from typing import Any
 
 from graphql.language.ast import BooleanValue, FloatValue, IntValue, StringValue