diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 191827526e890f..dd0ee59df3039d 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -4682,7 +4682,7 @@ can be used interchangeably to index the same dictionary entry.
 
       .. versionadded:: 3.8
 
-   .. method:: setdefault(key, default=None)
+   .. method:: setdefault(key, default=None, /)
 
       If *key* is in the dictionary, return its value.  If not, insert *key*
       with a value of *default* and return *default*.  *default* defaults to