diff --git a/graphene_sqlalchemy/enums.py b/graphene_sqlalchemy/enums.py
index f100be19..0adea107 100644
--- a/graphene_sqlalchemy/enums.py
+++ b/graphene_sqlalchemy/enums.py
@@ -1,3 +1,4 @@
+import six
 from sqlalchemy.orm import ColumnProperty
 from sqlalchemy.types import Enum as SQLAlchemyEnumType
 
@@ -62,7 +63,7 @@ def enum_for_field(obj_type, field_name):
     if not isinstance(obj_type, type) or not issubclass(obj_type, SQLAlchemyObjectType):
         raise TypeError(
             "Expected SQLAlchemyObjectType, but got: {!r}".format(obj_type))
-    if not field_name or not isinstance(field_name, str):
+    if not field_name or not isinstance(field_name, six.string_types):
         raise TypeError(
             "Expected a field name, but got: {!r}".format(field_name))
     registry = obj_type._meta.registry
diff --git a/graphene_sqlalchemy/fields.py b/graphene_sqlalchemy/fields.py
index 266b5f37..a9f514ba 100644
--- a/graphene_sqlalchemy/fields.py
+++ b/graphene_sqlalchemy/fields.py
@@ -1,6 +1,7 @@
 import warnings
 from functools import partial
 
+import six
 from promise import Promise, is_thenable
 from sqlalchemy.orm.query import Query
 
@@ -35,7 +36,7 @@ def model(self):
     def get_query(cls, model, info, sort=None, **args):
         query = get_query(model, info.context)
         if sort is not None:
-            if isinstance(sort, str):
+            if isinstance(sort, six.string_types):
                 query = query.order_by(sort.value)
             else:
                 query = query.order_by(*(col.value for col in sort))
diff --git a/graphene_sqlalchemy/registry.py b/graphene_sqlalchemy/registry.py
index acfa744b..c20bc2ca 100644
--- a/graphene_sqlalchemy/registry.py
+++ b/graphene_sqlalchemy/registry.py
@@ -1,5 +1,6 @@
 from collections import defaultdict
 
+import six
 from sqlalchemy.types import Enum as SQLAlchemyEnumType
 
 from graphene import Enum
@@ -42,7 +43,7 @@ def register_orm_field(self, obj_type, field_name, orm_field):
             raise TypeError(
                 "Expected SQLAlchemyObjectType, but got: {!r}".format(obj_type)
             )
-        if not field_name or not isinstance(field_name, str):
+        if not field_name or not isinstance(field_name, six.string_types):
             raise TypeError("Expected a field name, but got: {!r}".format(field_name))
         self._registry_orm_fields[obj_type][field_name] = orm_field