diff --git a/graphene/types/interface.py b/graphene/types/interface.py
index dbc3b476..f8227cdc 100644
--- a/graphene/types/interface.py
+++ b/graphene/types/interface.py
@@ -42,7 +42,7 @@ class Interface(BaseType):
         super(Interface, cls).__init_subclass_with_meta__(_meta=_meta, **options)
 
     @classmethod
-    def resolve_type(cls, instance, info):
+    def _resolve_type(cls, instance, info):
         from .objecttype import ObjectType
         if isinstance(instance, ObjectType):
             return type(instance)
diff --git a/graphene/types/typemap.py b/graphene/types/typemap.py
index b2bc4a0e..2b8856b0 100644
--- a/graphene/types/typemap.py
+++ b/graphene/types/typemap.py
@@ -194,8 +194,8 @@ class TypeMap(GraphQLTypeMap):
             return _type
 
         _resolve_type = None
-        if type.resolve_type:
-            _resolve_type = partial(resolve_type, type.resolve_type, map,
+        if type._resolve_type:
+            _resolve_type = partial(resolve_type, type._resolve_type, map,
                                     type._meta.name)
         return GrapheneInterfaceType(
             graphene_type=type,
@@ -216,8 +216,8 @@ class TypeMap(GraphQLTypeMap):
 
     def construct_union(self, map, type):
         _resolve_type = None
-        if type.resolve_type:
-            _resolve_type = partial(resolve_type, type.resolve_type, map,
+        if type._resolve_type:
+            _resolve_type = partial(resolve_type, type._resolve_type, map,
                                     type._meta.name)
 
         def types():
diff --git a/graphene/types/union.py b/graphene/types/union.py
index 45e03b0c..d1fab357 100644
--- a/graphene/types/union.py
+++ b/graphene/types/union.py
@@ -40,7 +40,7 @@ class Union(UnmountedType, BaseType):
         return cls
 
     @classmethod
-    def resolve_type(cls, instance, info):
+    def _resolve_type(cls, instance, info):
         from .objecttype import ObjectType  # NOQA
         if isinstance(instance, ObjectType):
             return type(instance)