diff --git a/Lib/pprint.py b/Lib/pprint.py
index 34ed12637e2..9314701db34 100644
--- a/Lib/pprint.py
+++ b/Lib/pprint.py
@@ -128,6 +128,9 @@ class PrettyPrinter:
         sort_dicts
             If true, dict keys are sorted.
 
+        underscore_numbers
+            If true, digit groups are separated with underscores.
+
         """
         indent = int(indent)
         width = int(width)