diff --git a/sphinx/config.py b/sphinx/config.py
index f3d1f7b39..87d5313ae 100644
--- a/sphinx/config.py
+++ b/sphinx/config.py
@@ -18,7 +18,7 @@ from os import path, getenv
 from typing import Any, NamedTuple, Union
 
 from six import (
-    PY2, PY3, iteritems, string_types, binary_type, text_type, integer_types, class_types
+    PY2, PY3, iteritems, string_types, binary_type, text_type, integer_types
 )
 
 from sphinx.deprecation import RemovedInSphinx30Warning
@@ -38,7 +38,7 @@ if False:
 logger = logging.getLogger(__name__)
 
 CONFIG_FILENAME = 'conf.py'
-UNSERIALIZABLE_TYPES = class_types + (types.ModuleType, types.FunctionType)
+UNSERIALIZABLE_TYPES = (type, types.ModuleType, types.FunctionType)
 copyright_year_re = re.compile(r'^((\d{4}-)?)(\d{4})(?=[ ,])')
 
 if PY3:
diff --git a/sphinx/ext/autodoc/__init__.py b/sphinx/ext/autodoc/__init__.py
index 4a1cb15ce..529d644ec 100644
--- a/sphinx/ext/autodoc/__init__.py
+++ b/sphinx/ext/autodoc/__init__.py
@@ -18,7 +18,7 @@ import warnings
 from typing import Any
 
 from docutils.statemachine import ViewList
-from six import iteritems, itervalues, text_type, class_types, string_types
+from six import iteritems, itervalues, text_type, string_types
 
 import sphinx
 from sphinx.deprecation import RemovedInSphinx30Warning
@@ -1061,7 +1061,7 @@ class ClassDocumenter(DocstringSignatureMixin, ModuleLevelDocumenter):  # type:
     @classmethod
     def can_document_member(cls, member, membername, isattr, parent):
         # type: (Any, unicode, bool, Any) -> bool
-        return isinstance(member, class_types)
+        return isinstance(member, type)
 
     def import_object(self):
         # type: () -> Any
@@ -1213,8 +1213,7 @@ class ExceptionDocumenter(ClassDocumenter):
     @classmethod
     def can_document_member(cls, member, membername, isattr, parent):
         # type: (Any, unicode, bool, Any) -> bool
-        return isinstance(member, class_types) and \
-            issubclass(member, BaseException)  # type: ignore
+        return isinstance(member, type) and issubclass(member, BaseException)
 
 
 class DataDocumenter(ModuleLevelDocumenter):
@@ -1345,7 +1344,7 @@ class AttributeDocumenter(DocstringStripSignatureMixin, ClassLevelDocumenter):
         # exported anywhere by Python
         return isdatadesc or (not isinstance(parent, ModuleDocumenter) and
                               not inspect.isroutine(member) and
-                              not isinstance(member, class_types))
+                              not isinstance(member, type))
 
     def document_members(self, all_members=False):
         # type: (bool) -> None