diff --git a/Doc/library/os.rst b/Doc/library/os.rst
index fbc7edb..7b37629 100644
--- a/Doc/library/os.rst
+++ b/Doc/library/os.rst
@@ -463,6 +463,8 @@
    True if the native OS type of the environment is bytes (eg. False on
    Windows).
 
+   .. versionadded:: 3.2
+
 
 .. function:: umask(mask)