diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 774b0c6230a..e491fd26daa 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -3828,7 +3828,7 @@ The constructors for both classes work the same:
 
    .. describe:: len(s)
 
-      Return the cardinality of set *s*.
+      Return the number of elements in set *s* (cardinality of *s*).
 
    .. describe:: x in s