diff --git a/doc/lispref/sequences.texi b/doc/lispref/sequences.texi
index 9869fe4c510..002a9ceceec 100644
--- a/doc/lispref/sequences.texi
+++ b/doc/lispref/sequences.texi
@@ -572,6 +572,21 @@ element of @var{sequence}.  The returned value is a list.
 @end example
 @end defun
 
+@defun seq-map-indexed function sequence
+  This function returns the result of applying @var{function} to each
+element of @var{sequence} and its index within @var{seq}.  The
+returned value is a list.
+
+@example
+@group
+(seq-map-indexed (lambda (elt idx)
+                   (list idx elt))
+                 '(a b c))
+@result{} ((0 a) (b 1) (c 2))
+@end group
+@end example
+@end defun
+
 @defun seq-mapn function &rest sequences
   This function returns the result of applying @var{function} to each
 element of @var{sequences}.  The arity of @var{function} must match