diff --git a/Lib/os.py b/Lib/os.py
index 2009025..52d3f1d 100644
--- a/Lib/os.py
+++ b/Lib/os.py
@@ -300,10 +300,11 @@
     (e.g., via del or slice assignment), and walk will only recurse into the
     subdirectories whose names remain in dirnames; this can be used to prune the
     search, or to impose a specific order of visiting.  Modifying dirnames when
-    topdown is false is ineffective, since the directories in dirnames have
-    already been generated by the time dirnames itself is generated. No matter
-    the value of topdown, the list of subdirectories is retrieved before the
-    tuples for the directory and its subdirectories are generated.
+    topdown is false has no effect on the behavior of os.walk(), since the
+    directories in dirnames have already been generated by the time dirnames
+    itself is generated. No matter the value of topdown, the list of
+    subdirectories is retrieved before the tuples for the directory and its
+    subdirectories are generated.
 
     By default errors from the os.scandir() call are ignored.  If
     optional arg 'onerror' is specified, it should be a function; it