diff --git a/graphene/core/classtypes/uniontype.py b/graphene/core/classtypes/uniontype.py
index 62003005..37a8d14a 100644
--- a/graphene/core/classtypes/uniontype.py
+++ b/graphene/core/classtypes/uniontype.py
@@ -35,6 +35,6 @@ class UnionType(six.with_metaclass(UnionTypeMeta, FieldsClassType)):
         return GraphQLUnionType(
             cls._meta.type_name,
             types=list(map(schema.T, cls._meta.types)),
-            resolve_type=cls._resolve_type,
+            resolve_type=lambda instance, info: cls._resolve_type(schema, instance, info),
             description=cls._meta.description,
         )