diff --git a/graphene/types/schema.py b/graphene/types/schema.py
index 8066de3e..7fd513b2 100644
--- a/graphene/types/schema.py
+++ b/graphene/types/schema.py
@@ -1,6 +1,6 @@
 import inspect
 
-from graphql import GraphQLSchema, graphql, is_type
+from graphql import GraphQLSchema, graphql, is_type, GraphQLObjectType
 from graphql.type.directives import (GraphQLDirective, GraphQLIncludeDirective,
                                      GraphQLSkipDirective)
 from graphql.type.introspection import IntrospectionSchema
@@ -12,6 +12,17 @@ from .objecttype import ObjectType
 from .typemap import TypeMap, is_graphene_type
 
 
+def assert_valid_root_type(_type):
+    if _type is None:
+        return
+    is_graphene_objecttype = inspect.isclass(
+        _type) and issubclass(_type, ObjectType)
+    is_graphql_objecttype = isinstance(_type, GraphQLObjectType)
+    assert is_graphene_objecttype or is_graphql_objecttype, (
+        "Type {} is not a valid ObjectType."
+    ).format(_type)
+
+
 class Schema(GraphQLSchema):
     '''
     Schema Definition
@@ -20,21 +31,23 @@ class Schema(GraphQLSchema):
     query and mutation (optional).
     '''
 
-    def __init__(self, query=None, mutation=None, subscription=None,
-                 directives=None, types=None, auto_camelcase=True):
-        assert inspect.isclass(query) and issubclass(query, ObjectType), (
-            'Schema query must be Object Type but got: {}.'
-        ).format(query)
+    def __init__(self,
+                 query=None,
+                 mutation=None,
+                 subscription=None,
+                 directives=None,
+                 types=None,
+                 auto_camelcase=True):
+        assert_valid_root_type(query)
+        assert_valid_root_type(mutation)
+        assert_valid_root_type(subscription)
         self._query = query
         self._mutation = mutation
         self._subscription = subscription
         self.types = types
         self.auto_camelcase = auto_camelcase
         if directives is None:
-            directives = [
-                GraphQLIncludeDirective,
-                GraphQLSkipDirective
-            ]
+            directives = [GraphQLIncludeDirective, GraphQLSkipDirective]
 
         assert all(isinstance(d, GraphQLDirective) for d in directives), \
             'Schema directives must be List[GraphQLDirective] if provided but got: {}.'.format(
@@ -61,7 +74,8 @@ class Schema(GraphQLSchema):
         '''
         _type = super(Schema, self).get_type(type_name)
         if _type is None:
-            raise AttributeError('Type "{}" not found in the Schema'.format(type_name))
+            raise AttributeError(
+                'Type "{}" not found in the Schema'.format(type_name))
         if isinstance(_type, GrapheneGraphQLType):
             return _type.graphene_type
         return _type
@@ -73,7 +87,8 @@ class Schema(GraphQLSchema):
             return _type
         if is_graphene_type(_type):
             graphql_type = self.get_type(_type._meta.name)
-            assert graphql_type, "Type {} not found in this schema.".format(_type._meta.name)
+            assert graphql_type, "Type {} not found in this schema.".format(
+                _type._meta.name)
             assert graphql_type.graphene_type == _type
             return graphql_type
         raise Exception("{} is not a valid GraphQL type.".format(_type))
@@ -102,4 +117,8 @@ class Schema(GraphQLSchema):
         ]
         if self.types:
             initial_types += self.types
-        self._type_map = TypeMap(initial_types, auto_camelcase=self.auto_camelcase, schema=self)
+        self._type_map = TypeMap(
+            initial_types,
+            auto_camelcase=self.auto_camelcase,
+            schema=self
+        )