diff --git a/Doc/library/warnings.rst b/Doc/library/warnings.rst
index 83163cc6882..e4942fa0c18 100644
--- a/Doc/library/warnings.rst
+++ b/Doc/library/warnings.rst
@@ -396,7 +396,7 @@ Available Functions
 -------------------
 
 
-.. function:: warn(message, category=None, stacklevel=1, source=None, *, skip_file_prefixes=None)
+.. function:: warn(message, category=None, stacklevel=1, source=None, *, skip_file_prefixes=())
 
    Issue a warning, or maybe ignore it or raise an exception.  The *category*
    argument, if given, must be a :ref:`warning category class <warning-categories>`; it