diff --git a/runtime/doc/digraph.txt b/runtime/doc/digraph.txt
index e9bdeb5..624aa27 100644
--- a/runtime/doc/digraph.txt
+++ b/runtime/doc/digraph.txt
@@ -1,4 +1,4 @@
-*digraph.txt*   For Vim version 9.0.  Last change: 2023 Mar 21
+*digraph.txt*   For Vim version 9.0.  Last change: 2023 Oct 20
 
 
 		  VIM REFERENCE MANUAL    by Bram Moolenaar
@@ -174,6 +174,13 @@
 The rouble sign was added in 2014 as 0x20bd.  Vim supports the digraphs =R and
 =P for this.  Note that R= and P= are other characters.
 
+QUADRUPLE PRIME
+
+The quadruple prime using the digraph 4' was added in 2023.  Although it is
+not part of RFC 1345, it supplements the existing digraph implementation as
+there already exist digraphs for PRIME, DOUBLE PRIME and TRIPLE PRIME using
+the 1', 2' and 3' digraphs.
+
 							*digraph-table*
 char  digraph	hex	dec	official name ~
 ^@	NU	0x00	  0	NULL (NUL)
@@ -931,6 +938,7 @@
 ′	1'	2032	8242	PRIME
 ″	2'	2033	8243	DOUBLE PRIME
 ‴	3'	2034	8244	TRIPLE PRIME
+⁗	4'	2057	8279	QUADRUPLE PRIME
 ‵	1"	2035	8245	REVERSED PRIME
 ‶	2"	2036	8246	REVERSED DOUBLE PRIME
 ‷	3"	2037	8247	REVERSED TRIPLE PRIME